Ionic Liquid, Lubricant, and Magnetic Recording Medium

ABSTRACT

A lubricant, which includes an ionic liquid including a conjugate base and a conjugate acid, wherein the conjugate acid has a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, a pKa of an acid that is a source of the conjugate base in acetonitrile is 10 or less, and solubility of the ionic liquid to CF 3 (CHF) 2 CF 2 CF 3  is 0.1 parts by mass relative to 100 parts by mass of CF 3 (CHF) 2 CF 2 CF 3 .

TECHNICAL FIELD

The present invention relates to an ionic liquid, a lubricant including the ionic liquid, and a magnetic recording medium using the lubricant.

BACKGROUND ART

Conventionally, in a thin film magnetic recording medium, a lubricant is applied onto a surface of a magnetic layer for the purpose of reducing frictions between a magnetic head and the surface of the magnetic recording medium, or reducing abrasion. In order to avoid adhesion, such as sticktion, an actual film thickness of the lubricant is of a molecular order. Accordingly, it is not exaggeration to say that the most important thing for a thin film magnetic recording medium is to select a lubricant giving excellent abrasion resistance in any environment.

During a life of a magnetic recording medium, it is important that a lubricant is present on a surface of the medium without causing desorption, spin-off, and chemical deteriorations. Making the lubricant present on a surface of a medium is more difficult, as the surface of the thin film magnetic recording medium is smoother. This is because the thin film magnetic recording medium does not have an ability of replenishing a lubricant as with a coating-type magnetic recording medium.

In the case where an adhesion force between a lubricant and a protective film disposed at a surface of a magnetic layer is weak, moreover, a film thickness of the lubricant is reduced during heating or sliding hence accelerating abrasion. Therefore, a large amount of the lubricant is required. The large amount of the lubricant becomes the mobile lubricant, and therefore a function of replenishing the lost lubricant can be provided. However, an excessive amount of the lubricant makes the film thickness of the lubricant larger than the surface roughness. Therefore, a problem associated with adhesion is caused, and in a crucial case, sticktion is caused, which is a factor of driving failures.

As illustrated in FIG. 1, moreover, an increase rate of an areal density of a hard disk drive of a product has been decreased in the last several years in NPL 1, but the year rate of 25% has been achieved. The areal density is nearly reaching 4 Tb/in², which is one of the targets. It can be found that a distance of a head-disk interface relative to an increase of the recording density has been reduced as illustrated in FIG. 2. There is always a need for improving reliability with the decrease in the head-disk interface distance, which has been described in NPLs 2 to 4.

A current recording density is about 1 Tb/in², spacing is about 6 nm, a thickness of a lubricant is about 0.8 nm, and the thickness of the lubricant needs to be reduced for a future recording density of 4 Tb/in². A molecular weight of a conventional PFPE lubricant needs to be made small in order to reduce a film thickness of the lubricant, but thermal stability may be deteriorated when the molecular weight is small. It can be understood that the problems in reliability cannot be sufficiently solved with a conventional perfluoropolyether (PFPE)-based lubricant.

Particularly for a thin film magnetic recording medium having high surface smoothness, a novel lubricant is designed at a molecular level, and synthesized to solve the above-described trade-off. Moreover, there are numbers of reports regarding lubricity of PFPE. As described, lubricants are very important in magnetic recording media.

Chemical structures of typical PFPE-based lubricants are depicted in Table 1.

TABLE 1 Fomblin-based lubricants X—CF₂(OCF₂CF₂)_(n)(OCF₂)_(m)OCF₂—X(0.5 < n/m < 1) Z X = —OCF₃ Z-DOL X = —CH₂OH Z-DIAC X = —COOH Z-Tetraol X = —CH₂ OCH₂CHCH₂ OH OH AM2001

Other lubricants A20H

Mono F—(CF₂CF₂CF₂O)₁—CF₂CF₂CH₂—N(C₃H₇)₂

Z-DOL in Table 1 is one of lubricants typically used for thin-film magnetic recording media. Moreover, Z-Tetraol (ZTMD) is a lubricant, in which a functional hydroxyl group is further introduced into a main chain of PFPE, and it has been reported that use of Z-Tetraol enhances reliability of a drive while reducing a space at an interface between a head and a medium. It has been reported that A20H suppresses decomposition of the PFPE main chain with Lewis acid or Lewis base, and improves tribological properties. On the other hand, it has been reported that Mono has a different polymer main chain and different polar groups to those of the PFPE, the polymer main chain and polar groups of Mono are respectively poly-n-propyloxy, and amine, and Mono reduces adhesion interactions at near contact.

However, a typical solid lubricant, which has a high melting point and is considered thermally stable, disturbs an electromagnetic conversion process that is extremely highly sensitive, and moreover, an abrasion powder scraped by a head is generated on a running track. Therefore, abrasion properties are deteriorated. As described above, the liquid lubricant has mobility that enables to move the adjacent lubricant layer to replenish the lubricant removed due to abrasion by the head. However, the lubricant is span-off from a surface of the disk especially at a high temperature during driving of the disk, because of the mobility of the lubricant, and thus the lubricant is reduced. As a result, a protection function is lost. Accordingly, a lubricant having a high viscosity and low volatility is suitably used, and use of such a lubricant enables to prolong a service life of a disk drive with suppressing an evaporation rate.

Considering the above-described lubricating systems, requirements for a low-friction and low-abrasion lubricant used for thin film magnetic recording media are as follows.

(1) Low volatility. (2) Low surface tension for a surface filling function. (3) Interaction between terminal polar groups and a surface of a disk. (4) High thermal and oxidization stability in order to avoid decomposition or reduction over a service period. (5) Chemically inactive with metals, glass, and polymers, and no abrasion powder generated by a head or a guide. (6) No toxicity and no flammability. (7) Excellent boundary lubricating properties. (8) Soluble with organic solvents.

Recently, an ionic liquid has been attracted attentions as one of solvents for synthesis of organic or inorganic materials and being friendly to the environments in the fields of electricity storage materials, a separation technology, and a catalyst technology. The ionic liquid is roughly classified as a molten salt having a low melting point. The ionic liquid is typically a molten salt having a melting point of 100° C. or lower, among the above-mentioned molten salts. The important properties of the ionic liquid used as a lubricant are low volatility, inflammability, thermal stability, and an excellent dissolving performance.

For example, abrasion and wear of a surface of a metal or ceramic may be reduced by using a certain ionic liquid compared to a conventional hydrocarbon-based lubricant. For example, there is a report that, in the case where an imidazole cation-based ionic liquid is synthesized by substituting with a fluoroalkyl group, and tetrafluoroboric acid salt or hexafluorophosphoric acid salt of alkyl imidazolium is used for steel, aluminium, copper, single crystal SiO₂, silicon, or sialon ceramics (Si—Al—O—N), tribological properties more excellent than those of cyclic phosphazene (X-1P) or PFPE are exhibited. Moreover, there is a report that an ammonium-based ionic liquid reduces frictions more than a base oil in the region of elastohydrodynamic to boundary lubrication. Moreover, effects of the ionic liquid as an additive for a base oil have been studied, and a chemical or tribochemical reaction of the ionic liquid has been researched to understand lubricating systems. However, there are almost no application examples of the ionic liquid to magnetic recording media that require lubricity properties at a molecular level.

It has been reported that, among ionic liquids, perfluorooctanoic acid alkyl ammonium salt is a protic ionic liquid (PIL), and has a significant effect of reducing frictions of a magnetic recording medium Compared to the above-mentioned Z-DOL (see, for example, PTLs 1 and 2, and NPLs 5 to 7).

However, the above-mentioned perfluorocarboxylic acid ammonium salts have weak interaction between a cation and an anion in the reaction represented by the following reaction formula (A). According to Le Chatelier's principle, the equilibrium of the reaction is sifted to the left side at a high temperature, and the perfluorocarboxylic acid ammonium salt becomes a dissociated neutral compound and hence thermal stability is deteriorated. Specifically, protons are transferred at a high temperature, the equilibrium is sifted to neutral substance and dissociation occurs (see, for example, NPL 8).

C_(n)F_(2n+1)COOH+C_(n)F_(2n+1)NH₂

C_(n)F_(2n+1)COO⁻H₃N⁺C_(n)H_(2n+1)  (A)

Meanwhile, the limit of a surface recording density of a hard disk is said to be from 1 Tb/in² to 2.5 Tb/in². Currently, the surface recording density is getting close to the limit, but developments of technology for increasing capacities have been actively conducted with a reduction in particle size of magnetic particles as a premise. As the technology for increasing capacities, there are a reduction in an effective flying height and introduction of Shingle Write (BMP).

Moreover, there is “thermally-assisted magnetic recording (heat assisted magnetic recording)” as the next-generation recording technology. The outline of the thermally-assisted magnetic recording is illustrated in FIG. 3. In FIG. 3, the referential numeral 1 is laser light, the referential numeral 2 is near field light, the referential numeral 3 is a recording head (PMR element), and the referential numeral 4 is a reproducing head (TMR element). The problems of the thermally-assisted magnetic recording include a deterioration of durability due to evaporation or deterioration of a lubricant on a surface of a magnetic layer because a recording area is heated by laser during recording and reproducing. Even though it is a short period, there is a possibility that a thin film magnetic recording medium is exposed to a high temperature, which is 400° C. or higher, in thermally-assisted magnetic recording. Therefore, there are concerns about thermal stability of a lubricant generally used for thin film magnetic recording media, such as Z-DOL and Z-TETRAOL.

A protic ionic liquid forms ions as described above, and is typically a material having high thermal stability. The equilibrium of the protic ionic liquid is represented by Scheme 1 below.

HA+H₂O

H₃O⁺+A⁻

B+H₂O

HB⁺+OH⁻

A⁻+HB⁺→A⁻HB⁺

HA+B+2H₂O

A⁻HB⁺+H₃O⁺+OH⁻

Scheme 1: Scheme of an Acid-Base Reaction

In Scheme 1, HA is Bronsted acid and B is Bronsted base. The acid (HA) and the base (B) are reacted as in Scheme 1 to generate a salt (A⁻HB⁺).

In Scheme 1, a dissociation constant K_(a1) of the acid and a dissociation constant K_(b2) of the base can be represented by Scheme 2 below in the form including the density.

$K_{a\; 1} = \frac{\left\lbrack A^{-} \right\rbrack \left\lbrack {H_{3}O^{+}} \right\rbrack}{\lbrack{HA}\rbrack}$ $K_{b\; 2} = \frac{\left\lbrack {HB}^{+} \right\rbrack \left\lbrack {OH}^{-} \right\rbrack}{\lbrack B\rbrack}$

Scheme 2: Relationship of Acid and Base Dissociation Constants

The K_(a1) and K_(b2) largely differ depending on a substance. In some cases, the K_(a1) and K_(b2) may be large digits, which is inconvenient for handling. Therefore, it is often represented with a negative logarithm. Specifically, the acid dissociation constant is determined as −log₁₀ K_(a1)=pK_(a1) as represented by Scheme 3 below. Clearly, acidity is stronger, as the pK_(a1) is smaller.

A difference ΔpKa of the acid dissociation constants of the acid and the base is discussed. The acid-base reaction is influenced by both acidity of the acid and basicity of the base (or acidity of conjugate acid of the base), and the difference ΔpKa in the acidity of the acid and base is represented by Scheme 3 below.

$\mspace{79mu} {{pK}_{a\; 1} = {{- \log}\frac{\left\lbrack A^{-} \right\rbrack \left\lbrack {H_{3}O^{+}} \right\rbrack}{\lbrack{HA}\rbrack}}}$ $\mspace{79mu} {{pK}_{b\; 2} = {{- \log}\frac{\left\lbrack {HB}^{+} \right\rbrack \left\lbrack {OH}^{-} \right\rbrack}{\lbrack B\rbrack}}}$ $\mspace{79mu} {{pK}_{a\; 2} = {{14 - {pK}_{b\; 2}} = {14 + {\log \frac{\left\lbrack {BH}^{+} \right\rbrack \left\lbrack {OH}^{-} \right\rbrack}{\lbrack B\rbrack}}}}}$ ${\Delta \; {pK}_{a}} = {{{pK}_{a\; 2} - {pK}_{a\; 1}} = {{{- {pK}_{a\; 1}} - {pK}_{b\; 2} + 14} = {{\log \frac{{{\left\lbrack A^{-} \right\rbrack \left\lbrack {BH}^{+} \right\rbrack}\left\lbrack {H_{3}O^{+}} \right\rbrack}\left\lbrack {OH}^{-} \right\rbrack}{\lbrack{HA}\rbrack \lbrack B\rbrack}} = {{\log \frac{\left\lbrack A^{-} \right\rbrack \left\lbrack {HB}^{+} \right\rbrack}{\lbrack{HA}\rbrack \lbrack B\rbrack}} = {\log \frac{\left\lbrack {A^{-}{HB}^{+}} \right\rbrack}{\lbrack{HA}\rbrack \lbrack B\rbrack}}}}}}$

Scheme 3: Relationship of pKa of Acid and Base

It is indicated that the ΔpKa increases, as the base concentration [A⁻HB⁺] increases relative to the acid concentration and the base concentration.

Meanwhile, Yoshizawa et al. have reported that proton transfer tends to occur when a difference (ΔpKa) of pKa of acid and base is 10 or greater,

[AH]+[B]⇔[A⁻HB⁺]

the equilibrium of the formula above is sifted to the ion side (right side), and stability is enhanced further (see, for example, NPL 8). Moreover, Watanabe et al. has reported that proton transfer and thermal stability of a protic ionic liquid largely depend on ΔpKa, and thermal stability of the ionic liquid is significantly improved by using the acid with which ΔpKa is 15 or greater when DBU (1,8-diazabicyclo[5,4,0]undec-7-ene) is used as a base (see NPL 9). Moreover, Kondo et al. have reported that a perfluorooctanesulfonic acid octadecyl ammonium salt-based protic ionic liquid having large ΔpKa improves durability of a magnetic recording medium (see NPL 10 and PTL 3). In the recent report of Kondo et al. related to thermal resistance of an ionic liquid, it has been reported that a decomposition temperature increases with up to certain degree of ΔpKa, and the decomposition temperature is not increased any further even when ΔpKa is increased from the above-described point (see NPLs 11 and 12). Moreover, it is reported that a pyrrolidinium-based ionic liquid including germinal dication may improve thermal resistance more than a typical ionic liquid of monocation (see NPL 13). As described in NPL 13, however, a relationship between a molecular structure constituting the pyrrolidinium-based ionic liquid and physical or chemical characteristics has not been fully understood yet. A combination of a cation and an anion largely influences on physical or chemical characteristics of an ionic liquid. A variety of the anion site is many, but the relationship could not be clarified unless the cation is a cation structurally similar to the anion (see, for example, NPL 14). For example, viscosity of the liquid increases, as hydrogen bonding strength of halogen is stronger (Cl>Br>I). However, the method for increasing the viscosity is not limited to the increase in the hydrogen bonding strength. For example, the viscosity can be increased by varying an alkyl chain of imidazole. Similarly, the combination of the anion and cation influences on a melting point, surface tension, and thermal stability, but a wide range of researches has not be conducted on an effect of the anion. Accordingly, it is possible to change physical or chemical characteristics of an ionic liquid by with a combination of cations or anions, but it is difficult to predict.

When application for hard disks is considered, moreover, an ionic liquid needs to be soluble to fluorine-based solvents (e.g., special solvent VERTREL, available from DuPont) used in production lines, as with commercially available perfluoropolyether. Note that, a fluorine-based solvent is suitably used as a solvent used for a lubricant in a production line of hard disks because the fluorine-based solvent does not required for the production line to be explosion proof. However, solubility of compounds for lubricants, other than a perfluoropolyether-based compound, to fluorine-based solvents is not very good. Therefore, use of such lubricants on hard disks has been limited even through lubricity of the lubricants is excellent.

CITATION LIST Patent Literatures

-   PTL 1: Japanese Patent (JP-B) No. 2581090 -   PTL 2: JP-B No. 2629725 -   PTL 3: International Publication No. WO 2014/104342

Non-Patent Literatures

-   NPL 1: Advances in Tribology, Volume 2013, Article ID 521086 -   NPL 2: C. M. Mate, Q. Dai, R. N. Payne, B. E. Knigge, and P.     Baumgart, “Will the numbers add up for sub-7-nm magnetic spacings?     Futuremetrology issues for disk drive lubricants, overcoats, and     topographies,” IEEE Transactions on Magnetics, vol. 41, no. 2, pp.     626-631, 2005. -   NPL 3: B. Marchon and T. Olson, “Magnetic spacing trends: from LMR     to PMR and beyond,” IEEE Transactions on Magnetics, vol. 45, no. 10,     pp. 3608-3611, 2009. -   NPL 4: J. Gui, “Tribology challenges for head-disk interface toward     1Tb/in2,” IEEE Transactions on Magnetics, vol. 39, no. 2, pp.     716-721, 2003. -   NPL 5: Kondo, H., Seto, J., Haga. S., Ozawa, K., (1989) Novel     Lubricants for Magnetic Thin Film Media, Magnetic Soc. Japan, Vol.     13, Suppl. No. S1, pp. 213-218 -   NPL 6: Kondo, H., Seki, A., Watanabe, H., & Seto, J., (1990).     Frictional Properties of Novel Lubricants for Magnetic Thin Film     Media, IEEE Trans. Magn. Vol. 26, No. 5, (September 1990), pp.     2691-2693, ISSN: 0018-9464 -   NPL 7: Kondo, H., Seki, A., & Kita, A., (1994a). Comparison of an     Amide and Amine Salt as Friction Modifiers for a Magnetic Thin Film     Medium. Tribology Trans. Vol. 37, No. 1, (January 1994), pp. 99-104,     ISSN: 0569-8197 -   NPL 8: Yoshizawa, M., Xu, W., Angell, C. A., Ionic Liquids by Proton     Transfer: Vapor pressure, Conductivity, and the Relevance of ΔpKa     from Aqueous Solutions, J. Am. Chem. Soc., Vol. 125, pp. 15411-15419     (2003) -   NPL 9: Miran, M. S., Kinoshita, H., Yasuda, T., Susan, M. A. B. H.,     Watanabe, M., Physicochemical Properties Determined by ΔpKa for     Protic Ionic Liquids Based on an Organic Super-strong Base with     Various Bronsted Acids, Phys. Chem. Chem. Phys., Vol 14, pp.     5178-5186 (2012) -   NPL 10: Hirofumi Kondo, Makiya Ito, Koki Hatsuda, KyungSung Yun and     Masayoshi Watanabe, “Novel Ionic Lubricants for Magnetic Thin Film”     Media, IEEE TRANSACTIONS ON MAGNETICS, VOL. 49, NO. 7, pp.     3756-3759, JULY (2013) -   NPL 11: Hirofumi Kondo, Makiya Ito, Koki Hatsuda, Nobuo Tano,     KyungSung Yun and Masayoshi Watanabe, IEEE International magnetic     conference Dresden, Germany, May 4-8, 2014 -   NPL 12: Hirofumi Kondo, Makiya Ito, Koki Hatsuda, Nobuo Tano,     KyungSung Yun and Masayoshi Watanabe, IEEE Trans. Magn., 2014, Vol.     50, Issue 11, Article#:3302504 -   NPL 13: Anderson, J. L., Ding R., Ellern A., Armstrong D. W.,     “Structure and Properties of High Stability Geminal Dicationic Ionic     Liquids”, J. Am. Chem. Soc., 2005, 127, 593-604. -   NPL 14: Dzyuba, S. V.; Bartsch, R. A., “Influence of Structural     Variations in 1-Alkyl(aralkyl)-3-Methylimidazolium     Hexafluorophosphates and Bis(trifluoromethylsulfonyl)imides on     Physical Properties of the Ionic Liquids, Chem. Phys. Phys. Chem.     2002, 3, 161-166

SUMMARY OF INVENTION Technical Problem

The present invention has been proposed based on the above-described situations in the art, and the present invention provides an ionic liquid having excellent lubricity at a high temperature and excellent applicability to production lines of magnetic recording media, a lubricant having excellent lubricity at a high temperature and excellent applicability to production lines of magnetic recording media, and a recording magnetic medium having excellent practical properties.

Solution to Problem

<1> A lubricant including:

an ionic liquid including a conjugate base and a conjugate acid, wherein the conjugate acid has a group including a straight-chain hydrocarbon group having 6 or more carbon atoms,

a pKa of an acid that is a source of the conjugate base in acetonitrile is 10 or less, and solubility of the ionic liquid to CF₃(CHF)₂CF₂CF₃ is 0.1 parts by mass or greater relative to 100 parts by mass of CF₃(CHF)₂CF₂CF₃. <2> The lubricant according to <1>, wherein the conjugate acid is represented by General Formula (A) below, General Formula (B) below, General Formula (C) below, General Formula (D) below, General Formula (E) below, or General Formula (F) below,

where, in General Formula (A), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and R² is a hydrogen atom or a hydrocarbon group, in General Formula (B), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, in General Formula (C), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, in General Formula (D), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and R² is a hydrogen atom or a hydrocarbon group, in General Formula (E), R³ is a hydrocarbon group, R⁴ is a hydrogen atom or a hydrocarbon group, and R⁵ is a group including a C8 or higher fluorinated hydrocarbon group including fluorinated hydrocarbon having 4 or more carbon atoms, and in General Formula (F), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and n is an integer of 1 or greater but 3 or less. <3> The lubricant according to <1> or <2>, wherein the conjugate base is represented by General Formula (X) below, General Formula (Y) below, or General Formula (Z) below,

where, in General Formula (X), l is an integer of 1 or greater but 12 or less, in General Formula (Y), n is an integer of 1 or greater but 12 or less, and in General Formula (Z), n is an integer of 0 or greater but 6 or less. <4> A magnetic recording medium including:

a non-magnetic support;

a magnetic layer disposed on the non-magnetic support; and

the lubricant according to any one of <1> to <3>, disposed on the magnetic layer.

<5> An ionic liquid including:

a conjugate base; and

a conjugate acid,

wherein the conjugate acid has a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, a pKa of an acid that is a source of the conjugate base in acetonitrile is 10 or less, and solubility of the ionic liquid to CF₃(CHF)₂CF₂CF₃ is 0.1 parts by mass or greater relative to 100 parts by mass of CF₃(CHF)₂CF₂CF₃. <6> The ionic liquid according to <5>, wherein the conjugate acid is represented by General Formula (A) below, General Formula (B) below, General Formula (C) below, General Formula (D) below, General Formula (E) below, or General Formula (F) below,

where, in General Formula (A), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and R² is a hydrogen atom or a hydrocarbon group, in General Formula (B), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, in General Formula (C), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, in General Formula (D), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and R² is a hydrogen atom or a hydrocarbon group, in General Formula (E), R³ is a hydrocarbon group, R⁴ is a hydrogen atom or a hydrocarbon group, R⁵ is a group including C8 or higher fluorinated hydrocarbon group including fluorinated hydrocarbon having 4 or more carbon atoms, and in General Formula (F), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and n is an integer of 1 or greater but 3 or less. <7> The ionic liquid according to <5> or <6>, wherein the conjugate base is represented by General Formula (X) below, General Formula (Y) below, or General Formula (Z) below,

where, in General Formula (X), l is an integer of 1 or greater but 12 or less, in General Formula (Y), n is an integer of 1 or greater but 12 or less, and in General Formula (Z), n is an integer of 0 or greater but 6 or less.

Advantageous Effects of Invention

The present invention can improve thermal stability of a lubricant, such as evaporation and thermal decomposition of the lubricant, and can maintain excellent lubricity over a long period. Moreover, the present invention can give excellent lubricity and improve practical properties, such as running performances, abrasion resistance, and durability, when the lubricant is used for a magnetic recording medium.

Furthermore, the present invention can provide a lubricant with which a production line does not need to be explosion proofed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph depicting transition and prediction of an areal recording density of a hard disk drive.

FIG. 2 is a roadmap of head-medium spacing relative to an areal recording density of a hard disk.

FIG. 3 is a schematic view illustrating thermally-assisted magnetic recording.

FIG. 4 is a cross-sectional view illustrating one example of a hard disk according to one embodiment of the present invention.

FIG. 5 is a cross-sectional view illustrating one example of a magnetic tape according to one embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be explained in details in the order below with reference to drawings, hereinafter.

1. Lubricant and ionic liquid 2. Magnetic recording medium

3. Examples 1. Lubricant and Ionic Liquid

A lubricant according to one embodiment of the present invention includes an ionic liquid including a conjugate acid and a conjugate base.

An ionic liquid according to one embodiment of the present invention includes a conjugate acid and a conjugate base.

In the ionic liquid, the conjugate acid has a group including a hydrocarbon group. The hydrocarbon group is a straight-chain hydrocarbon group having 6 or more carbon atoms. In the present specification, a “straight-chain hydrocarbon group having 6 or more carbon atoms” may be a partially-fluorinated hydrocarbon group where part of hydrogen atoms bonded to carbon atoms are substituted with fluorine atoms. Examples of the partially-fluorinated hydrocarbon group include a C8 or higher fluorinated hydrocarbon group including fluorinated hydrocarbon having 4 or more carbon atoms.

In the ionic liquid, a pKa of an acid that is a source of the conjugate base in acetonitrile is 10 or less.

Solubility of the ionic liquid to CF₃(CHF)₂CF₂CF₃ is 0.1 parts by mass or greater, preferably 0.3 parts by mass or greater, and more preferably 0.5 parts by mass or greater, relative to 100 parts by mass of CF₃(CHF)₂CF₂CF₃. The upper limit of the solubility is not particularly limited and may be appropriately selected depending on the intended purpose. As one example, the upper limit is 2.0 parts by mass, etc.

Note that, the solubility is solubility at 25° C.

Since the ionic liquid of the present embodiment includes a conjugate acid and a conjugate base and a pKa of an acid that is a source of the conjugate base in acetonitrile is 10 or less, the ionic liquid can exhibit excellent thermal stability. Since the ionic liquid has a group including a hydrocarbon group having 6 or more carbon atoms in a cation site, moreover, the ionic liquid can have excellent lubricity in combination with the thermal stability.

Since a certain amount of the ionic liquid is dissolved in CF₃(CHF)₂CF₂CF₃ that is often used as a fluorine-based solvent, moreover, a lubricant using a fluorine-based solvent can be produced with the ionic liquid. Use of such a lubricant can eliminate the necessity for providing a production line of magnetic recording media with explosion proof.

A lubricant including an ionic liquid typically used with the ionic liquid concentration of about 0.05% by mass or about 0.1% by mass. Therefore, solubility of the ionic liquid to a fluorine-based solvent needs to be 0.05% by mass or greater, preferably 0.1% by mass or greater. Moreover, the better solubility of the ionic liquid may be required depending on conditions for use. Taking conditions for use and storage conditions of the lubricant under consideration, moreover, the solubility of the ionic liquid needs to be 0.1% by mass or greater [0.1 parts by mass or greater of the ionic liquid is dissolved to 100 parts by mass of CF₃(CHF)₂CF₂CF₃], preferably 0.3% by mass or greater.

Note that, as a typical method, solubility to a solvent is analyzed with a solubility parameter, and materials having empirically similar solubility parameters tend to be mixed easily. Since there is an application limitation in estimation of solubility itself with an original solubility parameter value, however, it is often a case that the empirical values can be merely used for reference. Specifically, the above-described method is based on the regular solution theory, a modeling is performed only with intermolecular forces as forces affect between a solvent and a solute, and it is considered that an interaction for aggregating liquid molecules is only the intermolecular forces. However, it is rare that an actual solution is a regular solution. Faces other than intermolecular forces, such as hydrogen bonds, affect between the solvent-solute molecules. Whether the two components are mixed or cause a phase separation is thermodynamically determined with differences between the mixing enthalpy and mixing entropy of the two components. In case of an ionic liquid, it is extremely difficult to estimate solubility of the ionic liquid to a solvent, because the ionic liquid includes ions within a molecule.

The pKa is 10 or less, which is a strong acid, and is preferably 6.0 or less.

The lower limit of the pKa is not particularly limited and may be appropriately selected depending on the intended purpose, but the pKa is preferably −5.0 or greater.

In the present specification, the pKa is an acid dissociation constant and is an acid dissociation constant in acetonitrile.

<<Conjugate Base>>

The conjugate base is not particularly limited as long as a pKa of an acid that is a source of the conjugate base in acetonitrile is 10 or less, and the conjugate base may be appropriately selected depending on the intended purpose. Examples of the conjugate base include a conjugate base represented by General Formula (V) below, a conjugate base represented by General Formula (W) below, a conjugate base represented by General Formula (X) below, a conjugate base represented by General Formula (Y) below, and a conjugate base represented by General Formula (Z) below. Among the above-listed examples, a conjugate base represented by General Formula (X) below, a conjugate base represented by General Formula (Y) below, and a conjugate base represented by General Formula (Z) below are preferable, and a conjugate base represented by General Formula (X) below and a conjugate base represented by General Formula (Y) below are more preferable, because the above-mentioned conjugate bases can give high solubility of the ionic liquid to fluorine-based solvents.

In General Formula (X), 1 is an integer of 1 or greater but 12 or less, preferably an integer of 1 or greater but 6 or less, and more preferably an integer of 3 or greater but 6 or less.

In General Formula (Y), n is an integer of 1 or greater but 12 or less, and preferably an integer of 1 or greater but 6 or less.

In General Formula (Z), n is an integer of 0 or greater but 6 or less.

The acid that is a source of the conjugate base (hyaluronic acid: HA) is preferably Bronsted acid regarded as super acid, such as bis((perfluoroalkyl)sulfonyl)imide [(C_(l)F_(2l+1)SO₂)₂NH] (pKa=0 to 0.3), perfluorocyclopropane sulfoimide (pKa=−0.8), perfluoroalkyl sulfonic acid (C_(m)F_(2m+1)SO₃H) (pKa=0.7), tris(perfluoroalkanesulfonyl)methide compounds [(CF₃SO₂)₃CH] (pKa=−3.7), tricyanomethane (pKa=5.1), inorganic acids [e.g., nitric acid (pKa=9.4) and sulfuric acid (pKa=8.7)], tetrafluoroboric acid (pKa=1.8), and hexafluorophosphate, are preferable. For example, the pKa of the above-listed acids are introduced in J. Org. Chem. Vol. 76, No. 2, p. 394.

<<Conjugate Acid>>

The conjugate acid has a group including a straight-chain hydrocarbon group having 6 or more carbon atoms.

The number of carbon atoms of the hydrocarbon group is not particularly limited as long as the number of the carbon atoms is 6 or greater, and may be appropriately selected depending on the intended purpose. The number of the carbon atoms of the hydrocarbon group is preferably 10 or greater.

The upper limit of the number of carbon atoms of the straight-chain hydrocarbon group having 6 or more carbon atoms is not particularly limited and may be appropriately selected depending on the intended purpose. In view of availability of raw materials, the number of carbon atoms is preferably 30 or less, more preferably 25 or less, and particularly preferably 20 or less. Since the hydrocarbon group has a long chain, a friction coefficient is reduced to improve lubricity.

The group including a straight-chain hydrocarbon group having 6 or more carbon atoms is preferably the straight-chain hydrocarbon group having 6 or more carbon atoms.

However, solubility of the ionic liquid to a fluorine-based solvent may decrease when the number of carbon atoms is too large. Therefore, the number of carbon atoms is preferably determined with considering an effect of reducing a friction coefficient and solubility of the ionic liquid to a fluorine-based solvent.

The hydrocarbon group is not particularly limited as long as the hydrocarbon group is a straight-chain hydrocarbon group. The hydrocarbon group may be a saturated hydrocarbon group, an unsaturated hydrocarbon group having a double bond at part of the hydrocarbon group, or an unsaturated branched hydrocarbon group having a branched chain at part of the hydrocarbon group. Among the above-mentioned examples, the hydrocarbon group is preferably an alkyl group that is a saturated hydrocarbon group in view of abrasion resistance. Moreover, the hydrocarbon group is also preferably a straight-chain hydrocarbon group that does not have a branched chain at any part. Needless to say, the hydrocarbon group may be a hydrocarbon group that may have a branched chain at part of the hydrocarbon group.

Examples of the hydrocarbon group include a group represented by General Formula (I) below and a group represented by General Formula (II) below. Note that, the group represented by General Formula (II) corresponds to the partially-fluorinated hydrocarbon group.

—(CH₂)_(l)—CH₃  General Formula (I)

—(CH₂)_(m)—(CF₂)_(n)—CF₃  General Formula (II)

In General Formula (I), l is an integer of 5 or greater, preferably an integer of 9 or greater but 29 or less, more preferably an integer of 9 or greater but 24 or less, and particularly preferably an integer of 9 or greater but 19 or less.

In General Formula (II), m is an integer of 1 or greater but 6 or less and n is an integer of 3 or greater but 20 or less where m+n is 7 or greater. In General Formula (II), m is preferably an integer of 1 or greater but 3 or less and n is preferably an integer of 5 or greater but 10 or less.

The conjugate acid is preferably a conjugate acid represented by General Formula (A) below, a conjugate acid represented by General Formula (B) below, a conjugate acid represented by General Formula (C) below, a conjugate acid represented by General Formula (E) below, or a conjugate acid represented by General Formula (F) below, because the above-listed conjugate acids give a resultant ionic liquid excellent solubility against a fluorine-based solvent. Typically, it is a common knowledge that an ionic liquid having many hydrocarbon structures has low solubility to a fluorine-based solvent, but contrary to expectations, the conjugate acids of the following general formulae give a resultant ionic liquid excellent solubility to a fluorine-based solvent.

In General Formula (A), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and R² is a hydrogen atom or a hydrocarbon group.

In General Formula (B), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms.

In General Formula (C), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms.

In General Formula (D), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms and R² is a hydrogen atom or a hydrocarbon group.

In General Formula (E), R³ is a hydrocarbon group, R⁴ is a hydrogen atom or a hydrocarbon group, and R⁵ is a group including a C8 or higher fluorinated hydrocarbon group including fluorinated hydrocarbon having 4 or more carbon atoms.

In General Formula (F), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms and n is an integer of 1 or greater but 3 or less.

The number of carbon atoms of the hydrocarbon group of R¹ in General Formula (A), General Formula (B), General Formula (C), General Formula (D), and General Formula (F) is not particularly limited as long as the number is 6 or greater, and may be appropriately selected depending on the intended purpose. The number of carbon atoms of the hydrocarbon group of R¹ is preferably 10 or greater.

The upper limit of the number of carbon atoms of the hydrocarbon group of R¹ is not particularly limited and may be appropriately selected depending on the intended purpose. In view of availability of raw materials, the number of carbon atoms is preferably 30 or less, more preferably 25 or less, and particularly preferably 20 or less. Since the hydrocarbon group has a long chain, a friction coefficient is reduced to improve lubricity.

R¹ is preferably the straight-chain hydrocarbon group having 6 or more carbon atoms.

However, solubility of the ionic liquid to a fluorine-based solvent tends to decrease when the number of carbon atoms is too large. Therefore, the number of carbon atoms is preferably determined with considering an effect of reducing a friction coefficient and solubility of the ionic liquid to a fluorine-based solvent.

The hydrocarbon group of R¹ is not particularly limited as long as the hydrocarbon group is a straight-chain hydrocarbon group. The hydrocarbon group may a saturated hydrocarbon group, an unsaturated hydrocarbon group having a double bond at part of the hydrocarbon group, or an unsaturated branched hydrocarbon group having a branched chain at part of the hydrocarbon group. Among the above-mentioned examples, the hydrocarbon group is preferably an alkyl group that is a saturated hydrocarbon group in view of abrasion resistance. Moreover, the hydrocarbon group is also preferably a straight-chain hydrocarbon group that does not have a branched chain at any part.

Examples of R¹ include groups represented by General Formula (III) below.

—(CH₂)_(l)—CH₃  General Formula (III)

In General Formula (III), l is an integer of 5 or greater, preferably an integer of 9 or greater but 29 or less, and more preferably an integer of 9 or greater but 19 or less.

The hydrocarbon groups of R³ and R⁴ in General Formula (E) are not particularly limited and may be appropriately selected depending on the intended purpose. The hydrocarbon groups of R? and R⁴ are preferably hydrocarbon groups having 1 to 20 carbon atoms.

R⁵ in General Formula (E) is a group including a C8 or higher fluorinated hydrocarbon group including fluorinated hydrocarbon having 4 or more carbon atoms. Since the group of General Formula (E) is present, solubility of the ionic liquid to a fluorine-based solvent is improved.

R⁵ is preferably a group represented by General Formula (IV) below.

—(CH₂)_(m)—(CF₂)_(n)—CF₃  General Formula (IV)

In General Formula (IV), m is an integer of 1 or greater but 6 or less and n is an integer of 3 or greater but 20 or less, where m+n is 7 or greater. In General Formula (IV), m is preferably an integer of 1 or greater but 3 or less and n is an integer of 7 or greater but 10 or less. When the number of carbon atoms of the fluorinated hydrocarbon is too large, solubility of the ionic liquid reduces. Accordingly, the length of the chain of the fluorinated hydrocarbon is determined based on other constitutional elements within a molecule.

<<Preferable Examples of Ionic Liquid>>

The ionic liquid is preferably an ionic liquid represented by General Formula (1) below, an ionic liquid represented by General Formula (2) below, an ionic liquid represented by General Formula (3) below, an ionic liquid represented by General Formula (4) below, an ionic liquid represented by General Formula (5), or an ionic liquid represented by General Formula (6) below.

In General Formula (1), A⁻ is a conjugate base, R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and R² is a hydrogen atom or a hydrocarbon group.

In General Formula (2), A⁻ is a conjugate base, and R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms.

In General Formula (3), A⁻ is a conjugate base, and R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms.

In General Formula (4), A⁻ is a conjugate base, R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and R² is a hydrogen atom or a hydrocarbon group.

In General Formula (5), A⁻ is a conjugate base, R³ is a hydrocarbon group, R⁴ is a hydrogen atom or a hydrocarbon group, and R⁵ is a group including a C8 or higher fluorinated hydrocarbon group including fluorinated hydrocarbon group having 4 or more carbon atoms.

In General Formula (6), A⁻ is a conjugate base, R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and n is an integer of 1 or greater but 3 or less.

The ionic liquid represented by General Formula (1) is preferably an ionic liquid represented by General Formula (1-1) below or an ionic liquid represented by General Formula (1-2) below.

In General Formula (1-1), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, R² is a hydrogen atom or a hydrocarbon group, and l is an integer of 1 or greater but 12 or less.

The ionic liquid represented by General Formula (2) is preferably an ionic liquid represented by General Formula (2-1) below or an ionic liquid represented by General Formula (2-2) below.

In General Formula (2-1), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and l is an integer of 1 or greater but 12 or less.

In General Formula (2-2), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, n is an integer of 1 or greater but 12 or less.

The ionic liquid represented by General Formula (4) is preferably an ionic liquid represented by General Formula (4-1) below or an ionic liquid represented by General Formula (4-2) below.

In General Formula (4-1), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, R² is a hydrogen atom or a hydrocarbon group, and l is an integer of 1 or greater but 12 or less.

In General Formula (4-2), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, R² is a hydrogen atom or a hydrocarbon group, and n is an integer of 1 or greater but 12 or less.

The ionic liquid represented by General Formula (5) is preferably an ionic liquid represented by General Formula (5-1) below or an ionic liquid represented by General Formula (5-2) below.

In General Formula (5-1), R³ is a hydrocarbon group, R⁴ is a hydrogen atom or a hydrocarbon group, R⁵ is a group including a C8 or higher fluorinated hydrocarbon group including fluorinated hydrocarbon having 4 or more carbon atoms, and n is an integer of 1 or greater but 12 or less.

In General Formula (5-2), R³ is a hydrocarbon group, R⁴ is a hydrogen atom or a hydrocarbon group, R⁵ is a group including a C8 or higher fluorinated hydrocarbon group including fluorinated hydrocarbon having 4 or more carbon atoms, and l is an integer of 1 or greater but 12 or less.

The ionic liquid represented by General Formula (6) is preferably an ionic liquid represented by General Formula (6-1) below.

In General Formula (6-1), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, n is an integer of 1 or greater but 3 or less, and l is an integer of 1 or greater but 12 or less.

A preferable range of R¹ in the general formulae of the ionic liquid is identical to the preferable range of R¹ in the general formulae of the corresponding conjugate acid.

A preferable range of R² in the general formulae of the ionic liquid is identical to the preferable range of R² in the general formulae of the corresponding conjugate acid.

A preferable range of R³ in the general formulae of the ionic liquid is identical to the preferable range of R³ in the general formulae of the corresponding conjugate acid.

A preferable range of R⁴ in the general formulae of the ionic liquid is identical to the preferable range of R⁴ in the general formulae of the corresponding conjugate acid.

A preferable range of R⁵ in the general formulae of the ionic liquid is identical to the preferable range of R⁵ in the general formulae of the corresponding conjugate acid.

A preferable range of 1 in the conjugate base of the general formulae of the ionic liquid is identical to the preferable range of 1 in the corresponding conjugate base of the general formulae of the ionic liquid.

A preferable range of n in the conjugate base of the general formulae of the ionic liquid is identical to the preferable range of n in the corresponding conjugate base of the general formulae of the ionic liquid.

A synthesis method of the ionic liquid is not particularly limited and may be appropriately selected depending on the intended purpose. For example, various types of the ionic liquid can be synthesized with reference to a method described in Examples below.

The lubricant in the present embodiment may use the above-described ionic liquid alone, or may be used in combination with a lubricant known in the art. For example, the lubricant can be used in combination with long-chain carboxylic acid, long-chain carboxylic acid ester, perfluoroalkyl carboxylic acid ester, carboxylic acid perfluoroalkyl ester, perfluoroalkyl carboxylic acid perfluoroalkyl ester, a perfluoro polyether derivative.

In order to maintain a lubrication effect under severe conditions, moreover, an extreme-pressure agent may be used in combination at a blending ratio of about 30:70 to about 70:30 based on a mass ratio. The extreme-pressure agent performs a function of preventing friction and wear by reacting with a metal surface as a result of friction heat generated when a metal contact is partially formed in a boundary lubrication region, to form a reaction product coating film. As the extreme-pressure agent, for example, any of a phosphorous-based extreme-pressure agent, a sulfur-based extreme-pressure agent, a halogen-based extreme-pressure agent, an organic metal-based extreme-pressure agent, or a complex-based extreme-pressure agent can be used.

Moreover, an anti-rust agent may be used in combination according to the necessity. The anti-rust agent is not particularly limited as long as the anti-rust agent is an anti-rust agent that can be generally used for this type of a magnetic recording medium. Examples of the anti-rust agent include phenols, naphthols, quinones, heterocyclic compounds including a nitrogen atom, heterocyclic compounds including an oxygen atom, and heterocyclic compounds including a sulfur atom. Moreover, the anti-rust agent may be used by blending with a lubricant. Alternatively, the anti-rust agent may be deposited by dividing into 2 or more layers, for example, by forming a magnetic layer on a non-magnetic support, coating the upper part of the magnetic layer with an anti-rust agent layer, followed by coating with a lubricant layer.

As a solvent of the lubricant, moreover, a single or a combination of solvents, for example, alcohol-based solvents, such as isopropyl alcohol (IPA) and ethanol, can be used. For example, a hydrocarbon-based solvent, such as normal hexane, or a fluorine-based solvent may be used by mixing.

The solvent is preferably a fluorine-based solvent. Examples of the fluorine-based solvent include hydrofluoroethers [e.g., C₃F₇OCH₃, C₄F₉OCH₃, C₄F₉OC₂H₅, C₂F₅CF(OCH₃)C₃F₇, and CF₃(CHF)₂CF₂CF₃]. The hydrofluoroether may be used by mixing with alcohol, such as IPA, ethanol, and methanol.

The fluorine-based solvent may be a commercially available product. Examples of the commercially available product include: Novec™ 7000, 7100, 7200, 7300, and 71IPA, available from 3M; and Vertrel XF, and X-P10 available from Du Pont-Mitsui Fluorochemicals Company, Ltd.

2. Magnetic Recording Medium

Next, a magnetic recording medium using the above-described lubricant will be explained. The magnetic recording medium presented as one embodiment of the present invention include at least a magnetic layer on or above a non-magnetic support, and the above-described lubricant is deposited on or above the magnetic layer.

The lubricant in the present embodiment can be applied for a so-called a metal thin film magnetic recording medium, in which a magnetic layer is formed on a surface of a non-magnetic support by a method, such as vapor deposition and sputtering. Moreover, the lubricant can be also applied for a magnetic recording medium having a structure where an undercoat layer is disposed between a non-magnetic support and a magnetic layer. Examples of such a magnetic recording medium include magnetic disks and magnetic tapes.

FIG. 4 is a cross-sectional view illustrating one example of a hard disk. The hard disk has a structure where a substrate 11, an undercoat layer 12, a magnetic layer 13, a protective carbon layer 14, and a lubricant layer 15 are sequentially laminated.

Moreover, FIG. 5 is a cross-sectional view illustrating one example of a magnetic tape. The magnetic tape has a structure where a back-coating layer 25, a substrate 21, a magnetic layer 22, a protective carbon layer 23, and a lubricant layer 24 are sequentially laminated.

In the magnetic disk illustrated in FIG. 4, the substrate 11 and the undercoat layer 12 are corresponded to a non-magnetic support. In the magnetic tape illustrated in FIG. 5, the substrate 21 is corresponded to a non-magnetic support. When a substrate having rigidity, such as an Al alloy plate and a glass plate, is used as a non-magnetic support, a surface of the substrate may be hardened by forming an oxide film formed by anodizing, or a Ni—P coating on the surface of the substrate.

Each of the magnetic layers 13 and 22 is formed as a continuous film by a method, such as plating, sputtering, vacuum deposition, and plasma CVD. Examples of the magnetic layers 13 and 22 include: longitudinal magnetic recording metal magnetic films formed of metals (e.g., Fe, Co, and Ni), Co—Ni-based alloys, Co—Pt-based alloys, Co—Ni—Pt-based alloys, Fe—Co-based alloys, Fe—Ni-based alloys, Fe—Co—Ni-based alloys, Fe—Ni—B-based alloys, Fe—Co—B-based alloys, or Fe—Co—Ni—B-based alloys; and perpendicular magnetic recording metal magnetic thin films, such as Co—Cr-based alloy thin films, and Co—O-based thin films.

In the case where a longitudinal magnetic recording metal magnetic thin film is formed, particularly, a non-magnetic material, such as Bi, Sb, Pb, Sn, Ga, In, Ge, Si, and Tl, is formed as a base layer 12 on a non-magnetic support in advance, and a metal magnetic material is deposited through vapor deposition or sputtering in a perpendicular direction to diffuse the non-magnetic material into the magnetic metal thin film, to thereby improve a coercive force as well as eliminating orientation to assure in-plane isotropy.

Moreover, a hard protective layer 14 or 23, such as a carbon film, a diamond-formed carbon film, a chromium oxide film, and SiO₂ film, may be formed on a surface of the magnetic layer 13 or 22.

Examples of a method for applying the above-mentioned lubricant to such a metal thin film magnetic recording medium include a method for top-coating a surface of the magnetic layer 13 or 22, or a surface of the protective layer 14 or 23 with the lubricant, as illustrated in FIGS. 4 and 5. A coating amount of the lubricant is preferably from 0.1 mg/m² to 100 mg/m², more preferably from 0.5 mg/m² to 30 mg/m², and particularly preferably from 0.5 mg/m² to 20 mg/m².

As illustrated in FIG. 5, moreover, a metal thin film magnetic tape may optionally have a back-coating layer 25, other than a metal magnetic thin film, which is the magnetic layer 22.

The back-coating layer 25 is formed by adding a carbon-based powder for imparting conductivity, or an inorganic pigment for controlling a surface roughness to a resin binder, and applying the resin binder mixture. In the present embodiment, the above-described lubricant may be internally added to the back-coating layer 25, or applied to the back-coating layer 25 as top coating. Moreover, the above-described lubricant may be internally added to both the magnetic layer 22 and the back-coating layer 25, or applied to both the magnetic layer 22 and the back-coating layer 25 as top coating.

As another embodiment, moreover, the lubricant can be applied for a so-called coating-type magnetic recording medium, in which a magnetic coating film is formed as a magnetic layer by applying a magnetic coating material onto a surface of a non-magnetic support. In the coating-type magnetic recording medium, the non-magnetic support, a magnetic powder constituting the magnetic coating film, and the resin binder for use can be selected from any of those known in the art.

Examples of the non-magnetic support include: polymer supports formed by polymer materials, represented by polyesters, polyolefins, cellulose derivatives, vinyl-based resins, polyimides, polyamides, and polycarbonates; metal substrates formed of aluminium alloys, titanium alloys, etc.; ceramic substrates formed of alumina glass, etc.; and glass substrates. Moreover, a shape of the non-magnetic support is not particularly limited, and may be any form, such as a tape, a sheet, and a drum. Moreover, the non-magnetic support may be subjected to a surface treatment by which fine irregularities are formed, in order to control the surface texture of the non-magnetic support.

Examples of the magnetic powder include: ferromagnetic iron oxide-based particles, such as γ-Fe₂O₃, cobalt-coated γ-Fe₂O₃; ferromagnetic chromium dioxide; ferromagnetic metal-based particles formed of a metal, such as Fe, Co, and Ni, or an alloy containing any of the above-listed metals; and hexagonal ferrite particles in the form of hexagonal plates.

Examples of the resin binder include: polymers, such as vinyl chloride, vinyl acetate, vinyl alcohol, vinylidene chloride, acrylic acid ester, methacrylic acid ester, styrene, butadiene, and acrylonitrile; copolymers combining two or more selected from the above-listed polymers; polyurethane resins; polyester resins; and epoxy resins. In order to improve dispersibility of the magnetic powder, a hydrophilic polar group, such as a carboxylic acid group, a carboxyl group, and a phosphoric acid group, may be introduced into any of the above-listed binders.

Other than the magnetic powder and the resin binder, additives, such as a dispersing agent, an abrasive, an antistatic agent, and an anti-rust agent, may be added to the magnetic coating film.

As a method for retaining the above-described lubricant in the coating-type magnetic recording medium, there are a method where the lubricant is internally added to the magnetic layer constituting the magnetic coating film formed on the non-magnetic support, a method where the lubricant is applied on a surface of the magnetic layer as top coating, and a combination of the above-listed methods. In the case where the lubricant is internally added into the magnetic coating film, the lubricant is added in an amount of from 0.2 parts by mass to 20 parts by mass relative to 100 parts by mass of the resin binder.

In the case where a surface of the magnetic layer is top-coated with the lubricant, moreover, a coating amount of the lubricant is preferably from 0.1 mg/m² to 100 mg/m², and more preferably from 0.5 mg/m² to 20 mg/m². As a deposition method in the case where the lubricant is applied as top coating, the ionic liquid is dissolved in a solvent, and the obtained solution may be applied or sprayed, or a magnetic recording medium may be dipped in the solution.

The magnetic recording medium, to which the lubricant of the present embodiment is applied, exhibits excellent running performances, abrasion resistance, and durability because of a lubrication effect, and can further improve thermal stability.

EXAMPLES 3. Examples

Specific examples of the present invention will be explained hereinafter. In the examples, ionic liquids were synthesized, and lubricants each including the ionic liquid were produced. First, the solubility of each ionic liquid to VERTREL [CF₃(CHF)₂CF₂CF₃] that was a fluorine-based solvent was studied. Each of the lubricant solutions was applied to a surface of a magnetic disk and a surface of a magnetic tape, and disk durability and tape durability were evaluated. Production of a magnetic disk, a durability test of the disk, production of a magnetic tape, and a durability test of the tape were performed in the following manner. Note that, the present invention is not limited to these examples.

<Production of Magnetic Disk>

A magnetic thin film was formed on a glass substrate to produce a magnetic disk as illustrated in FIG. 4, for example, according to International Publication No. WO2005/068589. Specifically, a chemically reinforced glass disk, which was formed of aluminium silicate glass and had an outer diameter of 65 mm, an inner diameter of 20 mm, and a disk thickness of 0.635 mm, was prepared, and a surface of the glass disk was polished so that Rmax of the surface was to be 4.8 nm, and Ra of the surface was to be 0.43 nm. The glass substrate was subjected to ultrasonic cleaning for 5 minutes each in pure water and in isopropyl alcohol (IPA) having the purity of 99.9% or greater, and the washed glass substrate was left to stand in saturated IPA steam for 1.5 minutes, followed by drying. The resultant glass substrate was provided as a substrate 11.

On the substrate 11, a NiAl alloy (Ni: 50 mol %, Al: 50 mol %) thin film in the thickness of 30 nm as a seed layer, a CrMo alloy (Cr: 80 mol %, Mo: 20 mol %) thin film in the thickness of 8 nm as an undercoat layer 12, and a CoCrPtB alloy (Co: 62 mol %, Cr: 20 mol %, Pt: 12 mol %, B: 6 mol %) thin film in the thickness of 15 nm as a magnetic layer 13 were sequentially formed by DC magnetron sputtering.

Subsequently, a 5 nm-thick protective carbon layer 14 formed of amorphous diamond-like carbon was formed by plasma CVD, and the resultant disk sample was subjected to ultrasonic cleaning for 10 minutes in isopropyl alcohol (IPA) having the purity of 99.9% or greater inside a cleaner to remove impurities on a surface of the disk, followed by drying. Thereafter, a n-hexane/ethanol mixed solution of an ionic liquid was applied on a surface of the disk by dip coating in the environment of 25° C. and 50% in relative humidity (RH), to form about 1 nm of a lubricant layer 15.

<Thermal Stability Measurement>

A TG/DTA measurement was performed by means of EXSTAR6000 available from Seiko Instruments Inc. at a heating rate of 10° C./min and with a temperature range of from 30° C. to 600° C., while introducing air at a flow rate of 200 mL/min.

<Disk Durability Test>

A CSS durability test was performed by means of a commercially available strain-gauge-type disk friction-abrasion tester in the following manner. A hard disk was mounted on a rotatable spindle with tightening torque of 14.7 Ncm. Thereafter, a head slider was attached on the hard disk in a manner that a center of an air bearing surface at the inner circumference side of the head slider relative to the hard disk was 17.5 mm from a center of the hard disk. The head used for the measurement was an IBM3370-type inline head, a material of the slider was Al₂O₃—TiC, and the head load was 63.7 mN. In the test, the maximum value of friction force was monitored per CSS (contact, start, and stop) in the environment of 100 in cleanliness, 25° C., and 60% RH. The number of times when a coefficient of friction was greater than 1.0 was determined as a result of the CSS durability test. When a result of the CSS durability test was greater than 50,000, the result was represented as “>50,000.” Moreover, a CSS durability test was similarly performed after performing a heating test for 3 minutes at a temperature of 200° C., in order to study heat resistance.

<Production of Magnetic Tape>

A magnetic tape having a cross-sectional structure as illustrated in FIG. 5 was produced. First, Co was deposited on a substrate 21 formed of a 56 μm-thick MICTRON (aromatic polyamide) film available from TORAY INDUSTRIES, INC. by oblique deposition to form a magnetic layer 22 formed of a ferromagnetic metal thin film having a film thickness 100 nm. Next, a carbon protective layer 23 formed of 10 nm-thick diamond-like carbon was formed on a surface of the ferromagnetic metal thin film by plasma CVD, followed by cutting the resultant into a strip having a width of 6 mm. An ionic liquid dissolved in IPA was applied onto the carbon protective layer 23 in a manner that a film thickness of the ionic liquid solution was about 1 nm. In this manner, a lubricant layer 24 is formed to thereby produce a sample tape.

<Tape Durability Test>

Each sample tape was subjected to a measurement of still durability in an environment having a temperature of −5° C. and in an environment having a temperature of 40° C. and 30% RH, and measurements of a coefficient of friction and shuttle durability in an environment having a temperature of −5° C. and in an environment having a temperature of 40° C. and 90% RH. The still durability was evaluated by a decay time of an output in a paused state decayed by −3 dB. The shuttle resistant was evaluated by the number of shuttles taken until an output was reduced by 3 dB when repeated shuttle run was performed for 2 minutes per time. Moreover, a durability test was similarly performed after performing a heating test for 10 minutes at a temperature of 100° C., in order to study heat resistance.

The ionic liquid according to the present embodiment includes a conjugate base and a conjugate acid, where a pKa of an acid that is a source of the conjugate base in acetonitrile is 10 or less. Moreover, the cation site preferably includes a group including a hydrocarbon group having 6 or more carbon atoms. Thermal stability of such an ionic liquid, and durability of a magnetic recording medium using the ionic liquid were studied. Furthermore, solubility of the ionic liquid to a fluorine-based solvent was studied.

Example 1A Synthesis of bis(nonafluorobutanesulfonyl)imide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene

Synthesis of bis(nonafluorobutanesulfonyl)imide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene was prepared according to the following scheme.

According to the method disclosed by Matsumura et al., in the non-patent literature [N. Matsumura, H. Nishiguchi, M. Okada, and S. Yoneda, J. Heterocyclic Chem. pp. 885-887, Vol/23. Issue 3 (1986)], 6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene (6-octadecyl DBU) was synthesized.

To an ethanol solution of the obtained 6-octadecyl DBU (2.47 g), 11.84 g of a 30% bis(nonafluorobutanesulfonyl)imide aqueous solution was added. The resultant mixture was stirred for 1 hour at room temperature, followed by heating the mixture to reflux for 1 hour. After removing the solvent from the resultant, the residue was dissolved in dichloromethane, followed by sufficiently washing with water. After drying the organic layer with anhydrous sodium sulfate, the solvent was removed. The resultant was vacuum-dried for 3 days at 90° C. to thereby obtain 5.55 g of bis(nonafluorobutanesulfonyl)imide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene that was a colorless liquid. The yield was 92.2%.

In the present specification, the measurement of FTIR was performed by means of FT/IR-460 available from JASCO Corporation according to a transmission method using KBr plates or KBr pellets. The resolution of the measurement was 4 cm⁻¹.

The ¹H-NMR and ¹³C-NMR spectra were measured by means of Varian MercuryPlus 300 nuclear magnetic resonance spectrometer (available from Varian, Inc.). A chemical shift of ¹H-NMR was represented with a unit of ppm as a comparison with an internal standard (TMS at 0 ppm or deuterated solvent peak). Splitting patterns were described by denoting a singlet as s, a doublet as d, a triplet as t, a multiplet as m, and a broad peak as br.

The FTIR absorption of the generated product and the assignment are presented below.

Asymmetric stretching vibrations of SNS were observed at 1,042 cm⁻¹, symmetric stretching vibrations of SO₂ were observed at 1,091 cm⁻¹, symmetric stretching vibrations of CF₂ were observed at 1,164 cm⁻¹, asymmetric stretching vibrations of a SO₂ bond were observed at 1,360 cm⁻¹, stretching vibrations of C═N were observed at 1,633 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,848 cm⁻¹, and asymmetric stretching vibrations of CH₂ were observed at 2,920 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in CDCl₃ are presented below.

¹H-NMR (CDCl₃, δ ppm); 0.853 (t, 3H, J=6.6 Hz), 1.150-1.470 (m, 32H), 1.490-1.750 (m, 6H), 1.750-1.890 (m, 2H), 1.960-2.120 (2H, m), 2.700-2.800 (1H, m), 3.400-3.480 (m, 2H), 3.507 (t, J=6.0 Hz, 2H), 3.550-3.650 (m, 2H), 7.690 (brs, 1H)

¹³C-NMR (CDCl₃, δ ppm); 14.085, 19.199, 22.663, 25.502, 26.143, 27.105, 28.234, 28.982, 29.226, 29.349, 29.394, 29.501, 29.593, 29.639, 29.684, 31.913, 38.659, 43.375, 49.664, 53.953, 168.258

The generated product was determined as bis(nonafluorobutanesulfonyl)imide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene from the spectra above.

Note that, in bis(nonafluorobutanesulfonyl)imide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene, an acid [bis(nonafluorobutanesulfonyl)imide] that is a source of a conjugate base is 0.0 in acetonitrile.

Example 2A Synthesis of bis(nonafluorobutanesulfonyl)imide-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium

Synthesis of bis(nonafluorobutanesulfonyl)imide-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium was performed according to the following scheme.

A flask was charged with 7.13 g of DBU and 17.28 g of octadecylbromide, and the mixture was heated for 3 hours at 250° C. on a hot plate. When the resultant was cooled to room temperature, crystallization occurred. The obtained crystals were recrystallized with ethyl acetate, to thereby obtain 19.06 g of 8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undeceniumbromide in colorless crystals. The yield was 83.8%.

Peaks of a proton (¹H)NMR and a carbon (¹³C)NMR of the obtained compound in CDCl₃ are presented below.

¹H-NMR (CDCl₃, δ ppm); 0.826 (t, 3H, J=6.9 Hz), 1.180-1,310 (m, 30H), 1.530-1.640 (m, 2H), 1.710-1.810 (m, 6H), 2.100-2.170 (m, 2H), 2.850-2.910 (2H, m), 3.452-3.505 (m, 2H), 3.613 (t, J=7.5 Hz, 2H), 3.650-3.750 (m, 4H)

¹³C-NMR (CDCl₃, δ ppm); 13.918, 20.114, 22.465, 22.984, 25.930, 26.357, 28.234, 28.570, 28.982, 29.135, 29.242, 29.303, 29.394, 29.440, 29.486, 31.699, 47.252, 49,328, 54.182, 55.387, 166.259

The generated product was determined as 8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undeceniumbromide from the spectra above.

In heated water, 2.52 g of 8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undeceniumbromide was dissolved. To the resultant solution, an aqueous solution including 3.07 g of bis(nonafluorobutanesulfonyl)imide lithium salt was added. The resultant mixture was stirred for 1 hour at room temperature, followed by heating the mixture to reflux for 1 hour. After cooling the resultant reaction solution, extraction was performed on the reaction solution with dichloromethane, and the resultant was sufficiently washed with water until a result of a silver nitrate test became negative. After drying the organic layer with anhydrous sodium sulfate, the solvent was removed to thereby obtain 4.83 g of bis(nonafluorobutanesulfonyl)imide-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium that was a colorless liquid. The yield was 94.4%.

The FTIR absorption of the generated product and the assignment are presented below.

Asymmetric stretching vibrations of SNS were observed at 1,072 cm⁻¹, symmetric stretching vibrations of CF₂ were observed at 1,163 cm⁻¹, asymmetric stretching vibrations of a SO₂ bond were observed at 1,352 cm⁻¹, bending vibrations of CH₂ were observed at 1,469 cm⁻¹, symmetric stretching vibrations of C═N were observed at 1,626 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,852 cm⁻¹, and asymmetric stretching vibrations of CH₂ were observed at 2,922 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in CDCl₃ are presented below.

¹H-NMR (CDCl₃, δ ppm); 0.854 (t, 3H, J=6.6 Hz), 1.170-1.320 (m, 30H), 1.520-1.610 (m, 2H), 1.650-1.810 (m, 6H), 2.030-2.130 (m, 2H), 2.750-2.800 (2H, m), 3.380-3.440 (m, 2H), 3.450-3.540 (m, 4H), 3.580-3.630 (m, 2H)

¹³C-NMR (CDCl₃, δ ppm); 14.055, 19.855, 22.663, 22.953, 25.838, 26.433, 28.204, 28.433, 28.254, 29.059, 29.333, 29.394, 29.455, 29.562, 29.623, 29.669, 31.898, 46.977, 48.992, 54.121, 55.189, 166.381

The generated product was determined as bis(nonafluorobutanesulfonyl)imide-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium from the spectra above.

Note that, in bis(nonafluorobutanesulfonyl)imide-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium, a pKa of an acid [bis(nonafluoromethanesulfonyl)imide] that is a source of the conjugate base is 0.0 in acetonitrile.

Example 3A Synthesis of nonafluorobutanesulfonic acid-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium

Synthesis of nonafluorobutanesulfonic acid-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium was performed according to the following scheme.

In warm water, 3.11 g of 8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undeceniumbromide synthesized in the same manner as in Example 2A was dissolved. To the resultant solution, an aqueous solution including 2.17 g of potassium nonafluorobutanesulfonate was added. After stirring the resultant mixture for 1 hour at room temperature, the mixture was heated to reflux for 1 hour. After cooling the resultant reaction solution, extraction was performed on the reaction solution with dichloromethane, and the resultant was sufficiently washed with water until a result of a silver nitrate test became negative. After drying the organic layer with anhydrous sodium sulfate, the solvent was removed to thereby obtain 4.33 g of nonafluorobutanesulfonic acid-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium that was a colorless liquid. The yield was 95.9%.

The FTIR absorption of the generated product and the assignment are presented below.

Symmetric stretching vibrations of SO₂ were observed at 1,132 cm⁻¹, symmetric stretching vibrations of CF were observed at 1,230 cm⁻¹, asymmetric stretching vibrations of a SO₂ bond were observed at 1,259 cm⁻¹, bending vibrations of CH₂ were observed at 1,468 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,854 cm⁻¹, and asymmetric stretching vibrations of CH₂ were observed at 2,924 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in deuterated chloroform are presented below.

¹H-NMR (CDCl₃, δ ppm); 0.850 (t, 3H, J=6.6 Hz), 1.170-1.320 (m, 30H), 1.520-1.620 (m, 2H), 1.670-1.820 (m, 6H), 2.040-2.140 (m, 2H), 2.790-2.850 (2H, m), 3.417-3.470 (m, 2H), 3.490-3.600 (m, 4H), 3.620-3.670 (m, 2H)

¹³C-NMR (CDCl₃, δ ppm); 14.040, 19.992, 22.618, 23.045, 25.899, 26.464, 28.341, 28.494, 28.555, 29.089, 29.288, 29.379, 29.440, 29.532, 29.593, 29.639, 31.852, 46.993, 49.038, 54.105, 55.220, 166.488

The generated product was determined as nonafluorobutanesulfonic acid-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium from the spectra above.

Note that, in nonafluorobutanesulfonic acid-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium, a pKa of an acid (nonafluorobutanesulfonic acid) that is a source of the conjugate base is 0.7 in acetonitrile.

Example 4A Synthesis of bis(nonafluorobutanesulfonyl)imide-N-butyl-N-octadecylpyrrolidinium

Synthesis of bis(nonafluorobutanesulfonyl)imide-N-butyl-N-octadecylpyrrolidinium was performed according to the following scheme.

Into acetonitrile, 52.4 g of bromooctadecane and 8.75 g of potassium hydroxide were added. To the resultant mixture, 11.09 g of pyrrolidine was added. Thereafter, the resultant was heated to reflux for 24 hours. After performing filtration to separate the crystals, the solvent of the organic layer was removed. Thereafter, purification was performed by silica gel column chromatography using a mixed solvent of hexane and ethyl acetate, to thereby obtain 44.05 g of octadecyl pyrrolidine. The purity measured by gas chromatography was 99.0% or higher.

In acetonitrile, 5.04 g of octadecylpyrrolidine and 2.15 g of bromobutane were added. The resultant mixture was heated to reflux for 69 hours to allow the mixture to react. After completing the reaction, the reaction solution was cooled, and precipitated crystals were separated through filtration, followed by vacuum drying the crystals at 50° C., to thereby obtain 5.85 g of N-butyl-N-octadecylpyrrolidiniumbromide that was colorless crystals. The yield was 81.0%.

In warm water, 2.15 g of N-butyl-N-octadecylpyrrolidiniumbromide was dissolved. To the resultant solution, an ethanol/water mixed solution including 2.88 g of bis(nonafluorobutanesulfonyl)imide potassium salt was added. After stirring the resultant mixture for 1 hour at room temperature, the mixture was heated to reflux for 1 hour. After dissolving the precipitated reaction product in dichloromethane, the resultant was sufficiently washed with water until a result of a silver nitrate test became negative. After drying the organic layer with anhydrous sodium sulfate, the solvent was removed, followed by removing the solvent. Then the resultant was vacuum dried for 5 hours at 100° C. to thereby obtain 4.05 g of bis(nonafluorobutanesulfonyl)imide-N-butyl-N-octadecylpyrrolidinium that was pale yellow wax. The yield was 90.3%.

The FTIR absorption of the generated product and the assignment are presented below.

Asymmetric stretching vibrations of SNS were observed at 1,072 cm⁻¹, symmetric stretching vibrations of CF₂ were observed at 1,134 cm⁻¹, 1,165 cm⁻¹, 1,196 cm⁻¹, and 1,232 cm⁻¹, asymmetric stretching vibrations of SO₂ were observed at 1,352 cm⁻¹, bending vibrations of CH₂ were observed at 1,469 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,852 cm⁻¹, and asymmetric stretching vibrations of CH₂ were observed at 2,922 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in deuterated methanol are presented below.

¹H-NMR (δ ppm); 0.890 (t, 3H, J=6.9 Hz), 1.004 (t, 3H, J=6.9 Hz), 1.220-1.470 (m, 32H), 1.625-1.770 (m, 4H), 2.000-2.140 (m, 4H), 3.221-3.288 (m, 4H), 3.489-3.536 (m, 4H)

¹³C-NMR (δ ppm); 13.880, 14.444, 20.733, 22.824, 23.740, 24.213, 26.212, 27.418, 30.181, 30.486, 30.532, 30.608, 30.776, 33.081, 60.783, 60.997, 63.973

The generated product was determined as bis(nonafluorobutanesulfonyl)imide-N-butyl-N-octadecylpyrrolidinium from the spectra above.

Note that, in bis(nonafluorobutanesulfonyl)imide-N-butyl-N-octadecylpyrrolidinium, a pKa of an acid [bis(nonafluorobutanesulfonyl)imide] that is a source of the conjugate base is 0.0 in acetonitrile.

Example 5A Synthesis of bis(nonafluorobutanesulfonyl)imide-N-octadecylpyrrolidinium

Synthesis of bis(nonafluorobutanesulfonyl)imide-N-octadecylpyrrolidinium was performed according to the following scheme.

In ethanol, 2.69 g of octadecylpyrrolidine synthesized in the same manner as in Example 4A was dissolved. To the resultant solution, 16.15 g of a 30% bis(nonafluorobutanesulfonyl)imide aqueous solution was added. After completing the addition, the resultant mixture was stirred for 1 hour at room temperature, followed by heating the mixture to reflux for 1 hour. After removing the solvent from the mixture, the resultant was dissolved in dichloromethane, and the resultant was sufficiently washed with water, followed by removing the solvent. Recrystallization of the resultant was performed with a mixed solvent of n-hexane and ethanol, to thereby obtain 6.82 g of colorless crystals of bis(nonafluorobutanesulfonyl)imide-N-octadecylpyrrolidinium. The yield was 90.6%.

The FTIR absorption of the generated product and the assignment are presented below.

Asymmetric stretching vibrations of SNS were observed at 1,076 cm⁻¹, symmetric stretching vibrations of CF₂ were observed at 1,151 cm⁻¹, 1,213 cm⁻¹, and 1,232 cm⁻¹, asymmetric stretching vibrations of SO₂ were observed at 1,354 cm⁻¹, bending vibrations of CH₂ were observed at 1,469 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,852 cm⁻¹, asymmetric stretching vibrations of CH₂ were observed at 2,920 cm⁻¹, and stretching vibrations of NH were observed at 3,182 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in deuterated DMSO are presented below.

¹H-NMR (δ ppm); 0.855 (t, 3H, J=6.6 Hz), 1.140-1.330 (m, 30H), 1.650-1.780 (m, 2H), 2.050-2.200 (m, 4H), 2.810-2.960 (m, 2H), 3.000-3.110 (m, 2H), 3.710-3.810 (m, 2H), 7.750 (brs, 1H)

¹³C-NMR (δ ppm); 14.070, 22.663, 22.770, 25.731, 26.357, 28.921, 29.242, 29.349, 29.425, 29.532, 29.684, 31.913, 54.914, 56.532

The generated product was determined as bis(nonafluorobutanesulfonyl)imide-N-octadecylpyrrolidinium from the spectra above.

Note that, in bis(nonafluorobutanesulfonyl)imide-N-octadecylpyrrolidinium, a pKa of an acid [bis(nonafluorobutanesulfonyl)imide] that is a source of the conjugate base is 0.0 in acetonitrile.

Example 6A Synthesis of nonafluorobutanesulfonic acid-N-octadecylpyrrolidinium

Synthesis of nonafluorobutanesulfonic acid-N-octadecylpyrrolidinium was performed according to the following scheme.

In ethanol, 2.91 g of octadecylpyrrolidine synthesized in the same manner as in Example 4A was dissolved. To the resultant solution, 2.70 g of nonafluorobutane sulfonic acid were added. After completing the addition, the resultant mixture was stirred for 1 hour at room temperature, followed by heating the mixture to reflux for 1 hour. After removing the solvent from the mixture, the resultant was dissolved in dichloromethane, and the resultant was sufficiently washed with water, followed by removing the solvent. Recrystallization of the resultant was performed with a mixed solvent of n-hexane and ethanol, to thereby obtain 6.82 g of colorless crystal of nonafluorobutanesulfonic acid-N-octadecylpyrrolidinium (5.12 g). The yield was 91.3%.

The FTIR absorption of the generated product and the assignment are presented below.

Symmetric stretching vibrations of SO₂ were observed at 1,134 cm⁻¹, symmetric stretching vibrations of CF₂ were observed at 1,232 cm⁻¹, asymmetric stretching vibrations of SO₂ were observed at 1,352 cm⁻¹, bending vibrations of CH₂ were observed at 1,468 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,850 cm⁻¹, asymmetric stretching vibrations of CH₂ were observed at 2,918 cm⁻¹, and stretching vibrations of NH were observed at 3,076 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in deuterated DMSO are presented below.

¹H-NMR (δ ppm); 0.842 (t, 3H, J=6.6 Hz), 1.170-1.360 (m, 30H), 1.520-1.630 (m, 2H), 1.760-1.910 (m, 2H), 1.910-2.040 (m, 2H), 2.870-3.020 (m, 2H), 3.000-3.120 (m, 2H), 3.410-3.570 (m, 2H), 9.234 (brs, 1H)

¹³C-NMR (δ ppm); 14.089, 22.254, 22.697, 25.399, 26.085, 28.650, 28.879, 28.985, 29.107, 29.214, 31.473, 53.406, 54.154

The generated product was determined as nonafluorobutanesulfonic acid-N-octadecylpyrrolidinium from the spectra above.

Note that, in nonafluorobutanesulfonic acid-N-octadecylpyrrolidinium, a pKa of an acid (nonafluorobutanesulfonic acid) that is a source of the conjugate base is 0.7 in acetonitrile.

Example 7A Synthesis of trifluoromethanesulfonic acid-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium

Synthesis of trifluoromethanesulfonic acid-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium was performed according to the following scheme.

In heated water, 3.29 g of 8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undeceniumbromide synthesized in Example 2A was dissolved. To the resultant solution, an aqueous solution including 1.36 g of potassium trifluoromethane sulfonate was added. After stirring the resultant mixture for 1 hour at room temperature, the mixture was heated to reflux for 1 hour. After cooling the resultant reaction solution, the reaction solution was extracted with dichloromethane, and the resultant was sufficiently washed with water until a result of a silver nitrate test became negative. After drying the organic layer with anhydrous sodium sulfate, the solvent was removed to thereby obtain 3.74 g of trifluoromethanesulfonic acid-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium that was a colorless liquid. The yield was 99.5%. Recrystallization of the obtained trifluoromethanesulfonic acid-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium was performed using a mixed solvent of n-hexane and dichloromethane.

The FTIR absorption of the generated product and the assignment are presented below.

Symmetric stretching vibrations of a SO₂ bond were observed at 1,030 cm⁻¹, asymmetric stretching vibrations of a SO₂ bond were observed at 1,146 cm⁻¹, symmetric stretching vibrations of CF₃ were observed at 1,261 cm⁻¹, bending vibrations of CH₂ were observed at 1,448 cm⁻¹, symmetric stretching vibrations of C═N were observed at 1,624 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,848 cm⁻¹, and asymmetric stretching vibrations of CH₂ were observed at 2,916 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in CDCl₃ are presented below.

¹H-NMR (CDCl₃, δ ppm); 0.843 (t, J=6.6 Hz, 3H), 1.160-1.320 (m, 30H), 1.520-1.640 (m, 2H), 1.670-1.820 (m, 6H), 2.095 (quint, J=6.0 Hz, 2H), 2.790-2.850 (m, 2H), 3.416-3.470 (m, 2H), 3.490-3.600 (m, 4H), 3.610-3.680 (m, 2H)

¹³C-NMR (CDCl₃, δ ppm); 14.065, 20.048, 22.627, 23.070, 25.955, 26.474, 28.427, 28.519, 28.580, 29.114, 29.297, 29.389, 29.450, 29.542, 29.603, 29.648, 31.862, 47.048, 49.094, 54.146, 55.290, 166.513

The generated product was determined as trifluoromethanesulfonic acid-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium from the spectra above.

Note that, in trifluoromethanesulfonic acid-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium, a pKa of an acid (trifluoromethane sulfonic acid) that is a source of the conjugate base is 0.7 in acetonitrile.

Example 8A Synthesis of bis(nonafluorobutanesulfonyl)imide-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-octadecylimidazolium

Synthesis of bis(nonafluorobutanesulfonyl)imide-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-octadecylimidazolium was performed according to the following scheme.

In 100 mL of acetonitrile, 3 g of imidazole was dissolved. To the resultant solution, 14.9 g of octadecylbromide and 2.51 g of potassium hydroxide were added. The resultant mixture was heated with stirring to reflux for 4 hours, to thereby obtain 1-octadecylimidazole. After removing the solvent, the resultant was extracted with dichrolomethane, followed by performing purification through column chromatography. The resultant was analyzed by gas chromatography. As a result, the purity was 98.5% or higher.

At 90° C., 3.95 g of 1-octadecylimidazole and 7.29 g of 1′H,1′H,2′H,2′H-heptadecafluorodecyliodide were allowed to react for 65 hours. To the resultant, ethyl acetate was added. The precipitated crystals were separated through filtration, followed by drying, to thereby obtain 9.67 g of pale yellow crystals. Recrystallization of the obtained crystals was performed with ethyl acetate, to thereby obtain 8.67 g of colorless crystals.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in deuterated chloroform are presented below.

¹H-NMR (CDCl₃, δ ppm); 0.841 (t, 3H, J=6.6 Hz), 1.125-1.350 (m, 30H), 1.865-1.970 (m, 2H), 2.854-3.019 (m, 2H), 4.242-4.312 (2H, m), 4.855-4.898 (m, 2H), 7.325-7.337 (m, 1H), 7.608-7.620 (m, 1H), 10.196 (s, 1H)

¹³C-NMR (CDCl₃, δ ppm); 14.040, 22.633, 26.174, 28.891, 29.303, 29.440, 29.547, 29.608, 29.639, 29.959, 30.310, 31.608, 31.867, 42.689, 49.954, 50.641, 121.858, 122.942, 137.213

The generated product was determined as 1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-octadecylimidazoliumiodide from the spectra above.

Next, 3.29 g of 1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-octadecylimidazoliumiodide was dissolved in water. To the resultant solution, a solution obtained by dissolving 2.51 g of potassium bis(nonafluorobutanesulfonyl)imide in a mixed solvent of water and ethanol was added. The resultant mixture was heated to reflux for 2 hours. After cooling the resultant, the solvent was removed, followed by extraction with dichloromethane. The organic layer was washed with pure water until a result of the AgNO₃ test became negative. After drying the resultant with anhydrous sodium sulfate, the solvent was removed to thereby obtain 3.69 g of colorless crystals. Recrystallization of the obtained crystals were performed with a mixed solvent of n-hexane and ethanol, to thereby obtain 3.15 g of colorless crystals. The yield was 64%.

The FTIR absorption of the generated product and the assignment are presented below.

Symmetric stretching vibrations of a SO₂ bond were observed at 1,074 cm⁻¹, symmetric stretching vibrations of CF₂ were observed at 1,149 cm⁻¹ and 1,198 cm⁻¹, asymmetric stretching vibrations of a SO₂ bond were observed at 1,352 cm⁻¹, bending vibrations of CH₂ were observed at 1,469 cm⁻¹, symmetric stretching vibrations of C═N were observed at 1,564 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,850 cm⁻¹, asymmetric stretching vibrations of CH₂ were observed at 2,920 cm⁻¹, and stretching vibrations of CH of an imidazole ring were observed at 3,099 cm⁻¹ and 3,158 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in deuterated chloroform are presented below.

¹H-NMR (CDCl₃, δ ppm); 0.854 (t, 3H, J=6.6 Hz), 1.150-1.350 (m, 30H), 1.760-1.900 (m, 2H), 2.644-2.805 (m, 2H), 4.136-4.185 (m, 2H), 4.562-4.606 (m, 2H), 7.252-7.263 (m, 1H), 7.454-7.465 (m, 1H), 8.946 (s, 1H)

¹³C-NMR (CDCl₃, δ ppm); 14.024, 22.648, 26.006, 28.830, 29.247, 29.333, 29.440, 29.547, 29.669, 30.020, 31.913, 42.300, 50.457, 122.209, 123.003, 136.312

The generated product was determined as bis(nonafluorobutanesulfonyl)imide-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-octadecylimidazolium from the spectra above.

Note that, in bis(nonafluorobutanesulfonyl)imide-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-octadecylimidazolium, a pKa of an acid [bis(nonafluorobutanesulfonyl)imide] that is a source of the conjugate base is 0.0 in acetonitrile.

Example 9A Synthesis of bis(nonafluorobutanesulfonyl)imide-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-methylimidazolium

Synthesis of bis(nonafluorobutanesulfonyl)imide-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-methylimidazolium was performed according to the following scheme.

A flask was charged with 1.88 g of methylimidazole and 12.41 g of 1-1′H,1′H,2′H,2′H-heptadecafluorodecyliodide, and the resultant mixture was allowed to react for 2 hours at 80° C., with stirring with a magnetic stirrer in the sealed conditions. After cooling the resultant, the resultant was washed with ethyl acetate, and the solids were separated through filtration. Recrystallization of the solids was performed with a mixed solvent of ethyl acetate and ethanol, to thereby obtain 6.23 g of colorless crystals. The yield was 44%.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in deuterated chloroform are presented below.

¹H-NMR (CDCl₃, δ ppm); 2.976 (tt/J=7.2 Hz, 18.6 Hz, 2H), 3.955 (s, 3H), 4.643 (t/J=7.2 Hz, 2H), 7.618-7.630 (m, 1H), 7.766-7.772 (m, 1H), 9.095 (s, 1H)

¹³C-NMR (CDCl₃, δ ppm); 32.119 (t/J=21 Hz), 36.790, 43.032, 123.926, 125.315, 138.716

The generated product was determined as 1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-methylimidazoliumiodide from the spectra above.

In pure water, 2.06 g of 1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-methylimidazoliumiodide was dissolved. To the resultant solution, a solution obtained by dissolving 2.07 g of bis(nonafluorobutanesulfonyl)imide potassium salt in a mixed solvent of pure water and ethanol was added. The resultant mixture was allowed to react for 1 hour at room temperature, followed by heating the mixture to reflux for 1 hour. The precipitated product was separated through filtration, followed by sufficiently washing with water. After drying the resultant, recrystallization was performed with a mixed solvent of n-hexane and ethanol, to thereby obtain 2.41 g of colorless crystals. The yield was 67%.

The FTIR absorption of the generated product and the assignment are presented below.

Symmetric stretching vibrations of a SO₂ bond were observed at 1,072 cm⁻¹, symmetric stretching vibrations of CF₂ were observed at 1,147 cm⁻¹ and 1,176 cm⁻¹, asymmetric stretching vibrations of a SO₂ bond were observed at 1,352 cm⁻¹, symmetric stretching vibrations of C═N were observed at 1,577 cm⁻¹, and stretching vibrations of CH of an imidazole ring were observed at 3,097 cm⁻¹ and 3,157 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in deuterated chloroform are presented below.

¹H-NMR (CDCl₃, δ ppm); 2.836-3.020 (m, 2H), 3.934 (s, 3H), 4.613 (t/J=7.2 Hz, 2H), 7.597-7.604 (m, 1H), 7.736-7.742 (m, 1H), 9.095 (s, 1H)

¹³C-NMR (CDCl₃, δ ppm); 32.073 (t/J=21 Hz), 36.576, 42.941, 123.865, 125.254, 138.020

The generated product was determined as bis(nonafluorobutanesulfonyl)imide-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-methylimidazolium from the spectra above.

Note that, in bis(nonafluorobutanesulfonyl)imide-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-methylimidazolium, a pKa of an acid [bis(nonafluorobutanesulfonyl)imide] that is a source of the conjugate base was 0.0 in acetonitrile.

Example 10A Synthesis of nonafluorobutanesulfonic acid-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-methylimidazolium

Synthesis of nonafluorobutanesulfonic acid-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-methylimidazolium was performed according to the following scheme.

In pure water, 2.06 g of 1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-methylimidazoliumiodide synthesized in Example 9A was dissolved. To the resultant solution, a solution obtained by dissolving 1.10 g of potassium nonafluorobutanesulfonate in pure water was added. The resultant mixture was allowed to react for 1 hour at room temperature, followed by heating the mixture to reflux for 1 hour. After separating the precipitated product, the precipitated product was sufficiently washed with water. After drying the resultant, recrystallization was performed with a mixed solvent of n-hexane and ethanol, to thereby obtain 2.20 g of colorless crystals. The yield was 85%.

The FTIR absorption of the generated product and the assignment are presented below.

Symmetric stretching vibrations of a SO₂ bond were observed at 1,047 cm⁻¹, symmetric stretching vibrations of CF₂ were observed at 1,147 cm⁻¹ and 1,194 cm⁻¹, asymmetric stretching vibrations of a SO₂ bond were observed at 1,254 cm⁻¹, symmetric stretching vibrations of C═N were observed at 1,572 cm⁻¹, and stretching vibrations of CH of an imidazole ring were observed at 3,093 cm⁻¹ and 3,159 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in deuterated chloroform are presented below.

¹H-NMR (CDCl₃, δ ppm); 2.886-3.020 (m, 2H), 3.938 (s, 3H), 4.619 (t/J=7.2 Hz, 2H), 7.603-7.609 (m, 1H), 7.740-7.747 (m, 1H), 9.098 (s, 1H)

¹³C-NMR (CDCl₃, δ ppm); 32.027 (t/J=21 Hz), 36.576, 42.941, 123.850, 125.239, 138.060

The generated product was determined as nonafluorobutanesulfonic acid-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-methylimidazolium from the spectra above.

Note that, in nonafluorobutanesulfonic acid-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-methylimidazolium, a pKa of an acid (nonafluorobutanesulfonic acid) that is a source of the conjugate base is 0.7 in acetonitrile.

Example 11A Synthesis of 1,3-bis[bis(nonafluorobutanesulfonyl)imide-N-octadecylimidazolium)]propane

Synthesis of 1,3-bis[bis(nonafluorobutanesulfonyl)imide-N-octadecylimidazolium)]propane was performed according to the following scheme.

After allowing 1-octadecylimidazole (11.51 g) and 1,3-dibromopropane to react for 1 hour at 80° C. with stirring, the reaction was further performed for 3 hours by increasing the reaction temperature to 100° C. To the reaction product, ethyl acetate was added. The precipitated deposits were separated through filtration. After vacuum drying the deposits, recrystallization of the deposits were performed with a mixed solvent of n-hexane and ethanol, to thereby obtain 13.37 g of colorless crystals. The yield was 89%.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in deuterated chloroform are presented below.

¹H-NMR (CDCl₃, δ ppm); 0.820 (t/J=6.6 Hz, 6H) 1.100-1.350 (m, 60H) 1.800-1.920 (m, 4H), 2.852 (quint/J=7.2 Hz, 2H), 4.191 (t/J=7.2 Hz, 4H), 4.692 (t/J=7.2 Hz, 4H), 7.201-7.213 (m, 2H), 8.209-8.221 (m, 2H), 10.181 (s, 2H)

¹³C-NMR (CDCl₃, δ ppm); 14.022, 22.584, 26.217, 28.857, 29.254, 29.407, 29.498, 29.560, 29.605, 30.033, 30.811, 31.811, 46.700, 50.241, 121.291, 123.901, 136.447

The generated product was determined as 1,3-bis[1-octadecylimidazoliumbromide]propane from the spectra above.

In pure water, 2.49 g of 1,3-bis[1-octadecylimidazoliumbromide]propane was dissolved. To the resultant solution, an aqueous solution including 3.70 g of lithium bis(nonafluorobutanesulfonyl)imide was added. After reacting the resultant mixture for 1 hour at room temperature, the mixture was heated to reflux for 1 hour. After cooling the resultant, extraction was performed with dichloromethane, followed by the resultant was washed with pure water until a result of the AgNO₃ test became negative. After removing the solvent, recrystallization of the resultant was performed with a mixed solvent of n-hexane and ethanol to thereby obtain 4.80 g of colorless crystals. The yield was 85%.

The FTIR absorption of the generated product and the assignment are presented below.

Asymmetric vibrations of an SNS bond were observed at 1,072 cm⁻¹, symmetric stretching vibrations of CF₂ were observed at 1,167 cm⁻¹, asymmetric stretching vibrations of a SO₂ bond were observed at 1,352 cm⁻¹, bending vibrations of CH₂ were observed at 1,468 cm⁻¹, symmetric stretching vibrations of C═N were observed at 1,566 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,850 cm⁻¹, asymmetric stretching vibrations of CH₂ were observed at 2,920 cm⁻¹, and stretching vibrations of CH of an imidazole ring were observed at 3,120 cm⁻¹ and 3,155 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in deuterated chloroform are presented below.

¹H-NMR (CDCl₃, δ ppm); 0.854 (t/J=6.9 Hz, 6H), 1.150-1.350 (m, 60H), 1.780-1.900 (m, 4H), 2.481-2.587 (m, 2H), 4.098 (t/J=6.9 Hz, 4H), 4.359 (t/J=7.2 Hz, 4H), 7.189-7.200 (m, 2H), 7.600-7.610 (m, 2H), 8.333 (s, 2H)

¹³C-NMR (CDCl₃, δ ppm); 14.085, 22.679, 26.143, 28.799, 29.257, 29.349, 29.455, 29.547, 29.654, 29.684, 29.883, 31.470, 31.913, 46.413, 50.412, 122.057, 123.308, 135.458

The generated product was determined as 1,3-bis[bis(nonafluorobutanesulfonyl)imide-N-octadecylimidazolium)]propane from the spectra above.

Note that, in 1,3-bis[bis(nonafluorobutanesulfonyl)imide-N-octadecylimidazolium)]propane, a pKa of an acid [bis(nonafluorobutanesulfonyl)imide] that is a source of the conjugate base is 0.0 in acetonitrile.

Comparative Example 1A Synthesis of hexafluorocyclopropane-1,3-bis(sulfonyl)imide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium

For comparison, synthesis of hexafluorocyclopropane-1,3-bis(sulfonyl)imide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium was performed according to the following scheme by changing the acid of Example 1A from bis(nonafluorobutanesulfonyl)imide to hexafluorocyclopropane-1,3-bis(sulfonyl)imide.

To an ethanol solution including 2.18 g of 6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene synthesized in Example 1A, 3.00 g of hexafluorocyclopropane-1,3-bis(sulfonyl)imide was added. After stirring the resultant mixture for 1 hour at room temperature, the mixture was heated to reflux for 1 hour. After removing the solvent, the resultant was dissolved in dichloromethane, followed by sufficiently washing with water. After drying the organic layer with anhydrous sodium sulfate, the solvent was removed. The resultant was vacuum dried for 3 days at 90° C., to thereby obtain 4.86 g of hexafluorocyclopropane-1,3-bis(sulfonyl)imide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene that was a colorless liquid. The yield was 93.8%

The FTIR absorption of the generated product and the assignment are presented below.

Asymmetric stretching vibrations of SNS were observed at 1,042 cm⁻¹, symmetric stretching vibrations of SO₂ were observed at 1,091 cm⁻¹, symmetric stretching vibrations of CF₂ were observed at 1,164 cm⁻¹, asymmetric stretching vibrations of a SO₂ bond were observed at 1,360 cm⁻¹, stretching vibrations of C═N were observed at 1,633 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,848 cm⁻¹, asymmetric stretching vibrations of CH₂ were observed at 2,920 cm⁻¹, and stretching vibrations of NH were observed at 3,387 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in deuterated chloroform are presented below.

¹H-NMR (CDCl₃, δ ppm); 0.869 (t, 3H, J=6.6 Hz), 1.170-1.340 (m, 32H), 1.441-1.555 (m, 2H), 1.600-1.750 (m, 4H), 1.772-1.832 (m, 2H), 1.941-2.101 (m, 2H), 2.670-2.780 (m, 1H), 3.413 (t, 2H, J=6.6 Hz), 3.508 (t, 2H, J=6.6 Hz), 3.550-3.652 (m, 2H)

¹³C-NMR (CDCl₃, δ ppm); 14.055, 19.260, 22.633, 26.052, 27.090, 28.524, 29.120, 29.226, 29.318, 29.364, 29.486, 29.578, 29.608, 29.669, 31.867, 38.690, 43.177, 49.511, 53.861, 167.922

The generated product was determined as hexafluorocyclopropane-1,3-bis(sulfonyl)imide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium from the spectra above.

Note that, in hexafluorocyclopropane-1,3-bis(sulfonyl)imide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium, a pKa of an acid [hexafluorocyclopropane-1,3-bis(sulfonyl)imide] that is a source of the conjugate base is −0.8 in acetonitrile.

Comparative Example 2A Synthesis of heptadecafluorooctanesulfonic acid-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium

For comparison, synthesis of heptadecafluorooctanesulfonic acid-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium was performed according to the following scheme by changing of the acid of Example 1A from bis(nonafluorobutanesulfonyl)imide to heptadecafluorooctane sulfonic acid.

To an ethanol solution including 4.04 g of 6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene synthesized in Example 1A, 5.00 g of heptadecafluorooctane sulfonic acid was added. After stirring the resultant mixture for 1 hour at room temperature, the mixture was heated to reflux for 1 hour. After removing the solvent, the resultant was dissolved in dichloromethane, followed by sufficiently washed with water. The organic layer was dried with anhydrous sodium sulfate, followed by removing the solvent. Recrystallization of the resultant was performed with a mixed solvent of n-hexane and ethanol, to thereby obtain 7.86 g of heptadecafluorooctanesulfonic acid-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium. The yield was 86.9%

The FTIR absorption of the generated product and the assignment are presented below.

Symmetric stretching vibrations of SO₂ were observed at 1,055 cm⁻¹, symmetric stretching vibrations of CF₂ were observed at 1,252 cm⁻¹, asymmetric stretching vibrations of a SO₂ bond were observed at 1,368 cm⁻¹, bending vibrations of CH₂ were observed at 1,467 cm⁻¹, stretching vibrations of C═N were observed at 1,643 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,851 cm⁻¹, asymmetric stretching vibrations of CH₂ were observed at 2,920 cm⁻¹, and stretching vibrations of NH were observed at 3,296 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in deuterated chloroform are presented below.

¹H-NMR (CDCl₃, δ ppm); 0.843 (t, 3H, J=6.6 Hz), 1.205-1.287 (m, 32H), 1.544-1.800 (m, 8H), 1.975-2.033 (m, 2H), 2.792-2.816 (m, 1H), 3.440-3.559 (m, 6H), 8.713 (brs, 1H)

¹³C-NMR (CDCl₃, δ ppm); 14.024, 19.336, 22.633, 25.121, 26.311, 27.181, 28.311, 29.028, 29.303, 29.425, 29.532, 29.608, 29.654, 31.882, 38.491, 43.375, 49.725, 53.785, 168.029

The generated product was determined as heptadecafluorooctanesulfonic acid-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium from the spectra above.

Note that, in heptadecafluorooctanesulfonic acid-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium, a pKa of an acid [heptadecafluorooctane sulfonic acid] that is a source of the conjugate base is 0.7 in acetonitrile.

Comparative Example 3A Synthesis of tris(trifluoromethanesulfonyl)methide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium

For comparison, synthesis of tris(trifluoromethanesulfonyl)methide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium was performed according to the following scheme by changing the acid of Example 1A from bis(nonafluorobutanesulfonyl)imide to tris(trifluoromethanesulfonyl)methide.

In ethanol, 4.0 g of 6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene synthesized in the same manner as in Example 1A was dissolved. To the resultant solution, an ethanol diluted solution of 0.96 g of 65% concentrated nitric acid (d=1.400) was added to synthesize a nitric acid salt. The end point of the synthesis was checked and determined as a point where litmus paper indicated neutral. To the resultant, an ethanol solution of 4.45 g of tris(trifluoromethanesulfonyl)methide potassium salt was added, the mixture was stirred for 30 minutes, followed by heating the mixture to reflux for 30 minutes. After removing the solvent, extraction was performed with diethyl ether, and the organic layer was sufficiently washed with water. Thereafter, the resultant was dried with anhydrous sodium sulfate and the solvent was removed, to thereby obtain 7.60 g of tris(trifluoromethanesulfonyl)methide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium. The yield was 94.0%. Recrystallization of the obtained product was performed with a mixed solvent of n-hexane and ethanol.

The FTIR absorption of the generated product and the assignment are presented below.

Symmetric stretching vibrations of SO₂ were observed at 1,117 cm⁻¹, symmetric stretching vibrations of CF₃ were observed at 1,198 cm⁻¹, asymmetric stretching vibrations of a SO₂ bond were observed at 1,381 cm⁻¹, bending vibrations of CH₂ were observed at 1,470 cm⁻¹, stretching vibrations of C═N were observed at 1,632 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,850 cm⁻¹, asymmetric stretching vibrations of CH₂ were observed at 2,918 cm⁻¹, and stretching vibrations of NH were observed at 3,408 cm⁻¹.

Peaks of a proton (¹H)NMR and a carbon (¹³C)NMR of the obtained compound in CDCl₃ are presented below.

¹H-NMR (CDCl₃, δ ppm); 0.850 (t, 3H, J=6.6 Hz), 1.174-1.335 (m, 32H), 1.485-1.557 (m, 2H), 1.590-1.740 (m, 4H), 1.774-1.842 (m, 2H), 1.994-2.057 (m, 2H), 2.640-2.740 (m, 1H), 3.360-3.430 (m, 2H), 3.450-3.690 (m, 4H), 7.160 (brs, 1H)

¹³C-NMR (CDCl₃, δ ppm); 14.070, 19.122, 22.648, 25.899, 27.044, 28.463, 29.013, 29.165, 29.333, 29.455, 29.578, 29.669, 31.882, 38.644, 43.238, 49.481, 53.968, 120.126 (q, J=325 Hz), 168.197

The generated product was determined as tris(trifluoromethanesulfonyl)methide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium from the spectra above.

Note that, in tris(trifluoromethanesulfonyl)methide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium, a pKa of an acid [tris(trifluoromethanesulfonyl)methide] that is a source of the conjugate base is −3.7 in acetonitrile.

Comparative Example 4A Synthesis of hexafluorocyclopropane-1,3-bis(sulfonyl)imide-7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decenium

Synthesis of hexafluorocyclopropane-1,3-bis(sulfonyl)imide-7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decenium which had a 7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decene structure in a cation site and hexafluorocyclopropane-1,3-bis(sulfonyl)imide in an anion site was performed according to the following scheme.

First, synthesis of a raw material, 7-n-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decene (octadecyl TBD), will be described.

Synthesis was performed with reference to the method proposed by R. W. Alder et al. [see Non-Patent Literature, Roger W. Alder, Rodney W. Mowlam, David J. Vachon and Gray R. Weisman, “New Synthetic Routes to Macrocyclic Triamines,” J. Chem. Sos. Chem. Commun. pp. 507-508 (1992)].

Specifically, sodium hydride (55% by mass hexane) was added to 8.72 g of 1,5,7-triazabicyclo[4.4.0]-5-decene (TBD) dissolved in anhydrous THF at 10° C., and the resultant mixture was stirred. To the resultant, bromooctadecane was dripped over 20 minutes with maintaining the temperature to 10° C. Thereafter, the resultant was stirred for 30 minutes at 10° C., followed by stirring for 2 hours at room temperature. Thereafter, the resultant was heated to reflux for 1 hour. The resultant was returned to room temperature and a reaction was performed by adding an excessive amount of sodium hydride. After removing the solvent, column chromatography was performed using an amino-treated silica gel, to thereby obtain a pale yellow target.

In ethanol, 4.00 g of 7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decene that was the obtained target was dissolved. To the resultant solution, an ethanol solution of 3.00 g of hexafluorocyclopropane-1,3-bis(sulfonyl)imide was added. After stirring the resultant mixture for 30 minutes, the mixture was heated to reflux for 30 minutes. Thereafter, the solvent was removed, the resultant was dissolved in dichloromethane and sufficiently washed with water. Thereafter, the resultant was dried with anhydrous sodium sulfate, followed by removing the solvent, to thereby obtain 4.60 g of colorless hexafluorocyclopropane-1,3-bis(sulfonyl)imide-7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decenium. The yield was 92.0%. Recrystallization of the obtained product was performed with a mixed solvent of n-hexane and ethanol.

The FTIR absorption of the generated product and the assignment are presented below.

Asymmetric stretching vibrations of SNS were observed at 1,042 cm⁻¹, symmetric stretching vibrations of SO₂ were observed at 1,092 cm⁻¹, symmetric stretching vibrations of CF₂ were observed at 1,157 cm⁻¹, asymmetric stretching vibrations of a SO₂ bond were observed at 1,361 cm⁻¹, stretching vibrations of C═N were observed at 1,628 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,849 cm⁻¹, asymmetric stretching vibrations of CH₂ were observed at 2,921 cm⁻¹, and stretching vibrations of NH were observed at 3,412 cm⁻¹.

Peaks of a proton (¹H)NMR and a carbon (¹³C)NMR of the obtained compound in CDCl₃ are presented below.

¹H-NMR (CDCl₃, δ ppm); 0.847 (t, 3H, J=6.6 Hz), 1.222-1.274 (m, 30H), 1.460-1.600 (m, 2H), 1.969-2.055 (m, 4H), 3.210 (t, 2H, J=10 Hz), 3.310-3.409 (m, 8H), 5.931 (brs, 1H)

¹³C-NMR (CDCl₃, δ ppm); 14.055, 20.450, 20.740, 22.633, 26.494, 27.044, 29.226, 29.303, 29.425, 29.532, 29.608, 29.654, 31.867, 38.980, 46.428, 47.298, 47.786, 50.183, 150.385

The generated product was determined as hexafluorocyclopropane-1,3-bis(sulfonyl)imide-7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decenium from the spectra above.

Note that, in hexafluorocyclopropane-1,3-bis(sulfonyl)imide-7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decenium, a pKa of an acid [hexafluorocyclopropane-1,3-bis(sulfonyl)imide] that is a source of the conjugate base is −0.8 in acetonitrile.

Comparative Example 5A Synthesis of heptadecafluorooctanesulfonic acid-7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decenium

Synthesis of heptadecafluorooctanesulfonic acid-7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decenium which had a 7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decene structure in a cation site and heptadecafluorooctane sulfonic acid in an anion site was performed according to the following scheme.

In ethanol, 3.91 g of 7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decene synthesized in Comparative Example 4A was dissolved. To the resultant solution, an ethanol solution of 5.00 g heptadecafluorooctane sulfonic acid was added. After stirring the resultant mixture for 30 minutes, the mixture was heated to reflux for 30 minutes, followed by removing the solvent. The resultant was dissolved in dichrolomethane and a small amount of ethanol, and sufficiently washed with water. Thereafter, the resultant was dried with anhydrous sodium sulfate; followed by removing the solvent, to thereby obtain 8.50 g of colorless heptadecafluorooctanesulfonic acid-7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decenium. The yield was 95.4%. Recrystallization of the obtained product was performed with a mixed solvent of n-hexane and ethanol.

The FTIR absorption of the generated product and the assignment are presented below.

Symmetric stretching vibrations of CF were observed between 1,151 cm⁻¹ and 1,287 cm⁻¹, asymmetric stretching vibrations of a SO₂ bond were observed at 1,373 cm⁻¹, stretching vibrations of C═N were observed at 1,602 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,851 cm⁻¹, asymmetric stretching vibrations of CH₂ were observed at 2,924 cm⁻¹, and stretching vibrations of NH were observed at 3,289 cm⁻¹.

Peaks of a proton (¹H)NMR and a carbon (¹³C)NMR of the obtained compound in CDCl₃ are presented below.

¹H-NMR (CDCl₃, δ ppm); 0.841 (t, 3H, J=6.6 Hz), 1.205-1.239 (m, 30H), 1.460-1.590 (m, 2H), 1.915-2.060 (m, 4H), 3.254-3.316 (m, 8H), 3.390-3.450 (m, 2H), 7.158 (brs, 1H)

¹³C-NMR (CDCl₃, δ ppm); 14.041, 20.619, 20.970, 22.649, 26.419, 27.091, 29.319, 29.350, 29.502, 29.670, 31.883, 38.767, 46.368, 47.314, 47.986, 50.230, 150.417

The generated product was determined as heptadecafluorooctanesulfonic acid-7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decenium from the spectra above.

Note that, in heptadecafluorooctanesulfonic acid-7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decenium, a pKa of an acid [heptadecafluorooctane sulfonic acid] that is a source of the conjugate base is 0.7 in acetonitrile.

Comparative Example 6A Synthesis of hexafluorocyclopropane-1,3-bis(sulfonyl)imide-N-octadecylpyrrolidinium

Synthesis of hexafluorocyclopropane-1,3-bis(sulfonyl)imide-N-octadecylpyrrolidinium, which was an ionic liquid having a N-octadecylpyrrolidinium structure in a cation site but an anion site was changed to hexafluorocyclopropane-1,3-bis(sulfonyl)imide, different from Example 5A or Example 6A, was performed according to the following scheme.

In 2.68 g of octadecylpyrrolidine synthesized in the same manner as in Example 4A was dissolved. To the resultant solution, a solution obtained by dissolving 2.67 g of hexafluorocyclopropane-1,3-bis(sulfonyl)imide in ethanol was added. After completing the addition, the resultant mixture was stirred for 1 hour at room temperature, followed by heating the mixture to reflux for 1 hour. After removing the solvent, the resultant was dissolved in dichloromethane, sufficiently washed with water, and then dried with anhydrous magnesium sulfate, followed by removing the solvent, to thereby obtain 4.96 g of colorless solids. The yield was 92.8%. Recrystallization of the solids was performed with a mixed solvent of n-hexane and ethanol, to thereby obtain 4.10 g of colorless crystals of hexafluorocyclopropane-1,3-bis(sulfonyl)imide-N-octadecylpyrrolidinium.

The FTIR absorption of the generated product and the assignment are presented below.

Symmetric stretching vibrations of CF₂ were observed at 1,151 cm⁻¹, asymmetric stretching vibrations of SO₂ were observed at 1,354 cm⁻¹, bending vibrations of CH₂ were observed at 1,466 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,850 cm⁻¹, asymmetric stretching vibrations of CH₂ were observed at 2,918 cm⁻¹, and stretching vibrations of NH were observed at 3,192 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in deuterated DMSO are presented below.

¹H-NMR (δ ppm); 0.843 (t, 3H, J=6.6 Hz), 1.150-1.360 (m, 30H), 1.500-1.630 (m, 2H), 1.760-2.060 (m, 4H), 2.860-3.140 (m, 4H), 3.400-3.580 (m, 2H), 9.239 (brs, 1H)

¹³C-NMR (δ ppm); 14.119, 22.270, 22.697, 25.399, 26.101, 28.650, 28.879, 28.985, 29.107, 29.214, 31.473, 53.406, 54.154

The generated product was determined as hexafluorocyclopropane-1,3-bis(sulfonyl)imide-N-octadecylpyrrolidinium from the spectra above.

Note that, in hexafluorocyclopropane-1,3-bis(sulfonyl)imide-N-octadecylpyrrolidinium, a pKa of an acid [hexafluorocyclopropane-1,3-bis(sulfonyl)imide] that is a source of the conjugate base is −0.8 in acetonitrile.

Comparative Example 7A Synthesis of nonafluorobutanesulfonic acid-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-octadecylimidazolium

Synthesis of nonafluorobutanesulfonic acid-1-1-′H,1′H,2′H,2′H-heptadecafluorodecyl-3-octadecylimidazolium was performed according to the following scheme.

Next, 3.87 g of 1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-octadecylimidazoliumiodide synthesized in Example 8A was dissolved in water. To the resultant solution, a solution obtained by dissolving 1.76 g of potassium nonafluorobutanesulfonate in water was added. After stirring the resultant mixture for 1 hour at room temperature, the mixture was heated to reflux for 1 hour. After cooling the resultant, the solvent was removed, and extraction was performed with dichloromethane. The organic layer was washed with pure water until a result of the AgNO₃ test became negative. The resultant was dried with anhydrous sodium sulfate, the solvent was removed, and recrystallization of the resultant was performed with a mixed solvent of n-hexane and ethanol, to thereby obtain 4.20 g of colorless crystals. The yield was 91%.

The FTIR absorption of the generated product and the assignment are presented below.

Symmetric stretching vibrations of a SO₂ bond were observed at 1,147 cm⁻¹, symmetric stretching vibrations of CF₂ were observed at 1,200 cm⁻¹, bending vibrations of CH₂ were observed at 1,456 cm⁻¹, symmetric stretching vibrations of C═N were observed at 1,564 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,850 cm⁻¹, asymmetric stretching vibrations of CH₂ were observed at 2,916 cm⁻¹, and stretching vibrations of CH of an imidazole ring were observed at 3,113 cm⁻¹ and 3,150 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in deuterated chloroform are presented below.

¹H-NMR (CDCl₃, δ ppm); 0.849 (t/J=6.9 Hz, 3H), 1.160-1.380 (m, 30H), 1.860-1.970 (m, 2H), 2.620-3.010 (m, 2H), 4.254 (t/J=6.6 Hz, 2H), 4.845 (t/J=6.6 Hz, 2H), 7.276 (s, 1H), 7.526 (s, 1H), 10.184 (s, 1H)

¹³C-NMR (CDCl₃, δ ppm); 14.070, 22.648, 26.189, 28.906, 29.318, 29.455, 29.562, 29.623, 29.669, 29.990, 31.882, 32.691, 32.722, 42.719, 50.671, 121.706, 122.881, 137.503

The generated product was determined as nonafluorobutanesulfonic acid-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-octadecylimidazolium from the spectra above.

Note that, in nonafluorobutanesulfonic acid-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-octadecylimidazolium, a pKa of an acid (nonafluorobutanesulfonic acid) that is a source of the conjugate base is 0.7 in acetonitrile.

Comparative Example 8A Synthesis of bis(nonafluorobutanesulfonyl)imide-1-butyl-3-n-octadecylimidazolium

For comparison, synthesis of bis(nonafluorobutanesulfonyl)imide-1-butyl-3-n-octadecylimidazolium that was a monocationic ionic liquid was performed according to the following scheme.

In acetonitrile, 10.7 g of 1-octadecylimidazole and 6.03 g of bromobutane were dissolved. The resultant solution was heated to reflux for 5 hours. After removing the solvent, recrystallization was performed with a mixed solvent of n-hexane and ethanol, to thereby obtain 1-butyl-3-octadecylimidazoliumbromide. The obtained bromide (1.27 g) was dissolved in ethanol. To the resultant solution, an ethanol solution including 1.81 g of sodium bis(nonafluorobutanesulfonyl)imide was added. When the resultant mixture was stirred, colorless deposits were precipitated. The resultant solution was heated to reflux for 1 hour. After cooling the solution, the deposits were separated. The separated deposits were sufficiently washed with pure water, and recrystallization of the deposits was performed with a mixed solvent of n-hexane and ethanol, to thereby obtain 2.06 g of bis(nonafluorobutanesulfonyl)imide-1-butyl-3-n-octadecylimidazolium in the state of colorless crystals. The yield was 75%.

The FTIR absorption of the generated product and the assignment are presented below.

Symmetric stretching vibrations of SO₂ were observed at 1,072 cm⁻¹, symmetric stretching vibrations of CF₂ were observed at 1,137 cm-1 and 1,168 cm⁻¹, asymmetric stretching vibrations of a SO₂ bond were observed at 1,352 cm⁻¹, bending vibrations of CH₂ were observed at 1,469 cm⁻¹, stretching vibrations of C═N were observed at 1,564 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,850 cm⁻¹, asymmetric stretching vibrations of CH₂ were observed at 2,920 cm⁻¹, and stretching vibrations of CH of an imidazole ring were observed at 3,097 cm⁻¹ and 3,157 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in deuterated chloroform are presented below.

¹H-NMR (CDCl₃, δ ppm); 0.837 (t/J=6.6 Hz, 3H), 0.885 (t/J=7.2 Hz, 3H), 1.140-1.300 (m, 32H), 1.760 (quint/J=7.2 Hz, 4H), 4.112-4.173 (m, 4H), 7.776 (s, 1H), 7.781 (s, 1H), 9.175 (s, 1H)

¹³C-NMR (CDCl₃, δ ppm); 13.341, 14.043, 18.927, 22.239, 25.627, 28.466, 28.863, 28.970, 29.062, 29.184, 29.413, 31.443, 48.751, 49.026, 122.624, 136.101

The generated product was determined as bis(nonafluorobutanesulfonyl)imide-1-butyl-3-n-octadecylimidazolium from the spectra above.

Note that, in bis(nonafluorobutanesulfonyl)imide-1-butyl-3-n-octadecylimidazolium, a pKa of an acid [bis(nonafluorobutanesulfonyl)imide] that is a source of the conjugate base is 0.0 in acetonitrile.

Comparative Example 9A Synthesis of 1,5-bis[bis(nonafluorobutanesulfonyl)imide-1-octadecylimidazolium]pentane

Synthesis of 1,5-bis[bis(nonafluorobutanesulfonyl)imide-1-octadecylimidazolium]pentane was performed according to the following scheme.

In isopropanol, 10.00 g of 1-octadecylimidazole synthesized in Example 8A and 3.58 g of 1,5-dibromopentane were dissolved. A three-necked flask equipped with THREE-ONE MOTOR and a cooler was charged with the obtained water, and the liquid was heated to reflux for 3 hours. After removing the solvent, recrystallization was performed with a mixed solvent of ethyl acetate and ethanol to thereby obtain 12.82 g of colorless crystals of 1,5-bis(1-octadecylimidazoliumbromide)pentane. The yield was 94%.

In water, 1.93 g of 1,5-bis(1-octadecylimidazoliumbromide)pentane was dissolved. To the resultant solution, 2.76 g of bis(nonafluorobutanesulfonyl)imide potassium salt dissolved in water and a small amount of ethanol was added. After stirring the resultant mixture for 2 hours at room temperature, the mixture was heated to reflux for 2 hours. After completing the reaction, the resultant was filtered, followed by sufficiently washing with water until a result of the AgNO₃ test of the filtrate became negative. The resultant was vacuum dried for 10 hours at 70° C., to thereby obtain 4.00 g of a wax compound of 1,5-bis[bis(nonafluorobutanesulfonyl)imide-1-octadecylimidazolium]pentane. The yield was 96.5%.

The FTIR absorption of the generated product and the assignment are presented below.

Symmetric stretching vibrations of SO₂ were observed at 1,072 cm⁻¹, symmetric stretching vibrations of CF₂ were observed at 1,167 cm⁻¹, asymmetric stretching vibrations of a SO₂ bond were observed at 1,352 cm⁻¹, bending vibrations of CH₂ were observed at 1,468 cm⁻¹, stretching vibrations of C═N were observed at 1,566 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,854 cm⁻¹, and asymmetric stretching vibrations of CH₂ were observed at 2,924 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in deuterated DMSO are presented below.

¹H-NMR (deuterated DMSO, δ ppm); 0.828 (t, 6H, J=6.9 Hz), 1.130-1.340 (m, 62H), 1.710-1.880 (m, 8H), 4.106-4.169 (m, 8H), 7.750-7.761 (m, 2H), 7.772-7.782 (m, 2H), 9.141 (s, 2H)

¹³C-NMR (deuterated DMSO, δ ppm); 13.967, 22.239, 25.689, 28.543, 28.772, 28.879, 29.016, 29.138, 29.214, 29.520, 31.458, 48.675, 49.041, 122.594, 122.639, 136.086

The generated product was determined as 1,5-bis[bis(nonafluorobutanesulfonyl)imide-1-octadecylimidazolium]pentane from the spectra above.

Note that, in 1,5-bis[1-octadecylimidazolium-bis(nonafluorobutanesulfonyl)imide]pentane, a pKa of an acid [bis(nonafluorobutanesulfonyl)imide] that is a source of the conjugate base is 0.0 in acetonitrile.

Comparative Example 10A Synthesis of 1,9-bis[bis(nonafluorobutanesulfonyl)imide-1-octadecylimidazolium]nonane

Synthesis of 1,9-bis[bis(nonafluorobutanesulfonyl)imide-1-octadecylimidazolium]nonane was performed according to the following scheme.

In isopropanol, 10.91 g of 1-octadecylimidazole synthesized in Example 8A and 4.88 g of 1,9-dibromononane were dissolved. A three-necked flask equipped with THREE-ONE MOTOR and a cooler was charged with the obtained liquid, and the liquid was heated to reflux for 3 hours. After removing the solvent, recrystallization was performed with a mixed solvent of n-hexane and ethanol, to thereby obtain 14.11 g of colorless crystals of 1,9-bis(1-octadecylimidazoliumbromide)nonane. The yield was 89%.

In water, 3.00 g of 1,9-bis(1-octadecylimidazoliumbromide)nonane was dissolved. To the resultant solution, an aqueous solution including 4.04 g of bis(nonafluorobutanesulfonyl)imide lithium salt was added. After stirring the resultant mixture for 1 hour at room temperature, the mixture was heated to reflux for 2 hours. After completing the reaction, the crystals were separated through filtration. The crystals were sufficiently washed with water until a result of the AgNO₃ test of the filtrate became negative, to thereby obtain 5.16 g of 1,9-bis[bis(nonafluorobutanesulfonyl)imide-1-octadecylimidazolium]nonane. The yield was 73.7%.

The FTIR absorption of the generated product and the assignment are presented below.

Asymmetric stretching vibrations of SNS were observed at 1,072 cm⁻¹, symmetric stretching vibrations of CF₂ were observed at 1,169 cm⁻¹, asymmetric stretching vibrations of a SO₂ bond were observed at 1,352 cm⁻¹, bending vibrations of CH₂ were observed at 1,469 cm⁻¹, symmetric stretching vibrations of C═N were observed at 1,564 cm⁻¹, symmetric stretching vibrations of CH₂ were observed at 2,850 cm⁻¹, and asymmetric stretching vibrations of CH₂ were observed at 2,920 cm⁻¹.

Moreover, peaks of a proton (¹H)NMR and a carbon (¹³C)NMR in CDCl₃ are presented below.

¹H-NMR (CDCl₃, δ ppm); 0.870 (t/J=6.9 Hz, 6H), 1.180-1.370 (m, 70H), 1.780-1.920 (m, 8H), 4.151 (quin/J=7.2 Hz, 8H), 7.244-7.257 (m, 2H), 7.398-7.410 (m, 2H), 8.816 (s, 2H)

¹³C-NMR (CDCl₃, δ ppm); 14.055, 22.663, 25.334, 26.082, 27.807, 27.929, 28.845, 29.288, 29.333, 29.455, 29.562, 29.669, 29.730, 30.127, 31.898, 50.015, 50.091, 121.980, 122.621, 135.366

The generated product was determined as 1,9-bis[bis(nonafluorobutanesulfonyl)imide-1-octadecylimidazolium]nonane from the spectra above.

Note that, in 1,9-bis[bis(nonafluorobutanesulfonyl)imide-1-octadecylimidazolium]nonane, a pKa of an acid [bis(nonafluorobutanesulfonyl)imide] that is a source of the conjugate base is 0.0 in acetonitrile.

The ionic liquids synthesized in Examples and Comparative Examples above are summarized below.

Example 1B to Example 11B, and Comparative Example 1B to Comparative Example 10B <Measurement Results of Solubility to Fluorine-Based Solvent>

A solubility test was performed on the ionic liquid synthesized each of Examples and each of Comparative Examples using VERTREL XF [CF₃(CHF)₂CF₂CF₃] available from Du Pont-Mitsui Fluorochemicals Company, Ltd. as a fluorine-based solvent.

The ionic liquid was added to the predetermined mass of VERTREL XF. After applying ultrasonic waves to the resultant liquid for 5 minutes, the liquid was left to stand for 1 day, and the solubility of the ionic liquid was visually confirmed.

Specifically, 0.5 parts by mass or 0.1 parts by mass of each ionic liquid was added to 100 parts by mass of VERTREL XF (25° C.). After applying ultrasonic waves to the resultant mixture for 5 minutes, the resultant was left to stand for 1 day, and the solubility was visually observed and evaluated based on the following evaluation criteria.

Note that, a case where the mixture was visually observed to be transparent, the ionic liquid was judged as being dissolved. A case where the mixture was not transparent or insoluble matter was observed, the ionic liquid was judged as not being dissolved (insoluble).

The results are presented in Tables 2-1 to 2-2.

[Evaluation Criteria]

0.5% by mass or greater:

The ionic liquid was dissolved when 0.5 parts by mass of the ionic liquid was added.

0.1% by mass or greater but less than 0.5% by mass:

The ionic liquid was not dissolved when 0.5 parts by mass of the ionic liquid was added, but the ionic liquid was dissolved when 0.1 parts by mass of the ionic liquid was added.

Less than 0.1% by mass:

The ionic liquid was not dissolved both when 0.5 parts by mass of the ionic liquid was added and when 0.1 parts by mass of the ionic liquid was added.

TABLE 2-1 Synthesis Solubility to fluorine-based Example Example solvent Ex. 1B Ex. 1A 0.5% by mass or greater Ex. 2B Ex. 2A 0.5% by mass or greater Ex. 3B Ex. 3A 0.5% by mass or greater Ex. 4B Ex. 4A 0.5% by mass or greater Ex. 5B Ex. 5A 0.5% by mass or greater Ex. 6B Ex. 6A 0.1% by mass or greater but less than 0.5% by mass Ex. 7B Ex. 7A 0.5% by mass or greater Ex. 8B Ex. 8A 0.1% by mass or greater but less than 0.5% by mass Ex. 9B Ex. 9A 0.5% by mass or greater Ex. 10B Ex. 10A 0.1% by mass or greater but less than 0.5% by mass Ex. 11B Ex. 11A 0.5% by mass or greater

TABLE 2-2 Synthesis Solubility to fluorine-based Example Example solvent Comp. Ex. 1B Comp. Ex. 1A less than 0.1% by mass Comp. Ex. 2B Comp. Ex. 2A less than 0.1% by mass Comp. Ex. 3B Comp. Ex. 3A less than 0.1% by mass Comp. Ex. 4B Comp. Ex. 4A less than 0.1% by mass Comp. Ex. 5B Comp. Ex. 5A less than 0.1% by mass Comp. Ex. 6B Comp. Ex. 6A less than 0.1% by mass Comp. Ex. 7B Comp. Ex. 7A less than 0.1% by mass Comp. Ex. 8B Comp. Ex. 8A less than 0.1% by mass Comp. Ex. 9B Comp. Ex. 9A less than 0.1% by mass Comp. Ex. 10B Comp. Ex. 10A less than 0.1% by mass

The solubility of the ionic liquid of Example 1A to the fluorine-based solvent was 0.5% by mass or greater.

The solubility of the ionic liquid of Example 2A to the fluorine-based solvent was 0.5% by mass or greater.

The solubility of the ionic liquid of Example 3A to the fluorine-based solvent was 0.5% by mass or greater.

The solubility of the ionic liquid of Example 4A to the fluorine-based solvent was 0.5% by mass or greater.

The solubility of the ionic liquid of Example 5A to the fluorine-based solvent was 0.5% by mass or greater.

The solubility of the ionic liquid of Example 6A to the fluorine-based solvent was 0.1% by mass or greater but less than 0.5% by mass.

The solubility of the ionic liquid of Example 7A to the fluorine-based solvent was 0.5% by mass or greater.

The solubility of the ionic liquid of Example 8A to the fluorine-based solvent was 0.1% by mass or greater but less than 0.5% by mass.

The solubility of the ionic liquid of Example 9A to the fluorine-based solvent was 0.5% by mass or greater.

The solubility of the ionic liquid of Example 10A to the fluorine-based solvent was 0.1% by mass or greater but less than 0.5% by mass.

The solubility of the ionic liquid of Example 11A to the fluorine-based solvent was 0.5% by mass or greater.

The solubility of each of the ionic liquids of Comparative Examples 1A to 10A to the fluorine-based solvent was less than 0.1% by mass.

As it is clear from the results above, the ionic liquids used in Examples have solubility of 0.1% by mass or greater relative to VERTREL XF that was a fluorine-based solvent, and the solubility of the ionic liquids was sufficient for use in production of hard disks.

Even in the case where the ionic liquids had the same 6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene skeleton, moreover, the ionic liquid having bis(nonafluorobutanesulfonyl)imide as an anion as in Example 1B had more excellent solubility compared to the case of hexafluorocyclopropane-1,3-bis(sulfonyl)imide (Comparative Example 1B), heptadecafluorooctane sulfonic acid (Comparative Example 2B), or tris(trifluoromethanesulfonyl)methide (Comparative Example 3B).

Even in the case where the ionic liquids had the same 6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene skeleton, moreover, the ionic liquid having trifluoromethane sulfonic acid as an anion as in Example 7B had more excellent solubility compared to the case of hexafluorocyclopropane-1,3-bis(sulfonyl)imide (Comparative Example 1B) or heptadecafluorooctane sulfonic acid (Comparative Example 2B).

However, the fluorine contents contained in the molecular weights of the anion sites were 0.589, 0.389, 0.649, and 0.372, respectively, as presented in Table 3. When the anion site was heptadecafluorooctane sulfonic acid having a high fluorine content, solubility of the ionic liquid was low. However, the solubility of the ionic liquid cannot be merely assumed with the fluorine content of the anion site. It can be understood that the bis(nonafluorobutanesulfonyl)imide-based ionic liquid improved solubility to a fluorine-based solvent.

TABLE 3 Fluorine content Name of acid Structural formula (mass) trifluoromethane sulfonic acid CF₃SO₃H 0.380 bis(nonafluorobutanesulfonyl)imide (C₄F₉SO₂)₂NH 0.589 nonafluorobutane sulfonic acid C₄F₉SO₃H 0.570 tris(trifluoromethanesulfonyl)methide (CF₃SO₂)₃CH 0.372 heptadecafluorooctane sulfonic acid C₈F₁₇SO₃H 0.646 hexafluorocyclopropane-1,3- CF₂(CF₂SO₂)₂NH 0.389 bis(sulfonyl)imide

With comparing Example 8B to Comparative Example 7B, moreover, the solubility was improved when the imidazole structure of the cation site was the same but the anion site was changed from sulfonic acid to sulfonyl imide. With comparing Example 8B to Comparative Example 8B, solubility was improved because of the molecular design where fluorinated carbon was introduced to the 1st position of the butyl group. Overall, it could be understood that solubility of nonafluorobutanesulfonic acid, which was the acid of the bis(nonafluorobutanesulfonyl)imide-based ionic liquid, improved solubility to a fluorine-based solvent.

In Examples 9B and 10B, moreover, the fluorine content of an entire molecule was increased by replacing the octadecyl group of Example 8B with a methyl group, thus solubility was improved and the ionic liquids of Examples 9B and 10B were dissolved even when the ionic liquid was the sulfonic acid salt where the anion site was the sulfonic acid.

Example 11B, Comparative Example 9B, and Comparative Example 10B are for comparing dications. The lengths of the bonding groups of Example 11B, Comparative Example 9B, and Comparative Example 10B were 3, 5, and 9, respectively. As a result, it was found that solubility to a fluorine-based solvent could be improved when the length of the bonding group was short.

Regarding solubility of an ionic liquid to a fluorine-based solvent, the following insight was obtained from the result of the researches conducted by the present inventors.

It was found that solubility of the ionic liquids having the same octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene structure was different depending on the position at which an octadecyl group was introduced. Specifically, among the ionic liquids, in which the octadecyl group was introduced at the 6^(th) position, only the ionic liquid having the bis(nonafluorobutanesulfonyl)imide structure as an anion was dissolved. As it could be seen from Examples 2B and 3B, among the ionic liquids, in which the octadecyl group was introduced at the 8^(th) position, not only the ionic liquid having the bis(nonafluorobutanesulfonyl)imide structure, but also the ionic liquid having the perfluorosulfonic acid structure (Comparative Example 2B), which was not dissolved in case of the octadecyl group at the 6^(th) position, were dissolved. Specifically, it was found that solubility of the ionic liquid was improved by introducing the octadecyl group at the 8^(th) position.

In the case of the ionic liquid having 7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decene as a cation structure, the ionic liquid of Comparative Example 4A having hexafluorocyclopropane-1,3-bis(sulfonyl)imide as an anion structure or the ionic liquid of Comparative Example 5A having heptadecafluorooctane sulfonic acid as an anion structure were not dissolved. In Comparative Example 3A, tris(trifluoromethanesulfonyl)methide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene was not dissolved. Moreover, it is assumed also based on the results of other researches not introduced in the present specification that solubility of an ionic liquid having 7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decene as a cation structure is higher than solubility of an ionic liquid having 6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene as a cation structure.

It was found that solubility of ionic liquids each having an octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene structure was different depending on an anion structure of the ionic liquid. Specifically, it was found that, in the case where the anion of the ionic liquid was hexafluorocyclopropane-1,3-bis(sulfonyl)imide or heptadecafluorooctane sulfonic acid, the ionic liquid was not dissolved, but the ionic liquid was dissolved when the anion was trifluoromethane sulfonic acid. In this case, the solubility cannot be explained with a fluorine content of the anion site.

Among the ionic liquids each having a 1-heptadecafluorodecylimidazole skeleton, the ionic liquid having a structure having a methyl group at the 3^(rd) position had more excellent solubility than the ionic liquid having a structure having an octadecyl group, and such an ionic liquid was dissolved in VERTREL XF even when the nonafluorobutanesulfonic acid salt was included in combination. In this case, it is assumed that solubility of the ionic liquid was improved because a fluorine content of an entire molecule was increased by replacing the long-chain hydrocarbon with the methyl group.

In case of dication, the understanding of the results was trickier. When the number of the bond chain was 9 or 5, the solubility was less than 0.1% by mass. The solubility was improved only when the number of the bond chain was 3. In case of the ionic liquid having a N-butyl-N-octadecylpyrrolidine skeleton having a pyrrolidone skeleton, the solubility of the ionic liquid to a fluorine-based solvent was 0.5% by mass or greater, but the solubility was deteriorated to less than 0.1% by mass when the ionic liquid had dication. In case of the imidazole skeleton, however, it was found that the ionic liquid with a monocation of butyl-octadecylimidazole had solubility of less than 0.1% by mass to a fluorine-based solvent, but solubility of the ionic liquid was improved by replacing the monocation with dication.

Although it was not discussed in the present specification, moreover, most of imidazole-based ionic liquids having a long-chain alkyl group are not dissolved in a fluorine-based solvent. However, it was found that among pyrrolidine-based ionic liquids, the ionic liquids that could be dissolved in a fluorine-based solvent were Example 4A, Example 5A, and Example 6A, and the pyrrolidine-based ionic liquids were easily dissolved.

Accordingly, solubility of the cation sites and the anion sites to a fluorine-based solvent is summarized, and the order of the better solubility of the cation sites and the order of the better solubility of the anion sites are as follows.

In General Formula (A-1), General Formula (A-2), General Formula (B), General Formula (C), and General Formula (D), R¹ and R² are as described earlier.

In General Formula (A-1), R²¹ is a hydrocarbon group.

In General Formula (E), R¹, R², and R³ are each independently a hydrogen atom or a long-chain hydrocarbon group, with the proviso that at least one of R¹, R², and R³ is a long-chain hydrocarbon group.

In General Formula (X), l is as described earlier.

In General Formulae (Y) and (Z), n is as described earlier.

Accordingly, as a combination of an acid and a base in an ionic liquid, the following acid and base are preferable. As the base, a pyrrolidine [General Formula (D)], octadecyldiazabicyclo[5.4.0]-7-undecene [General Formula (B), General Formula (A-1), General Formula (A-2)], or 1,5,7-triazabicyclo[4.4.0]-5-decene [General Formula (C)] skeleton, in which an alkyl group is introduced at a nitrogen atom, is preferably used. As the acid, perfluoroalkanesulfonylimide [General Formula (X)] or perfluorosulfonic acid [General Formula (Y)] having a short alkyl chain is preferably used.

Example 1C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of bis(nonafluorobutanesulfonyl)imide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene were 352.9° C., 378.2° C., and 396.7° C., respectively. Compared to the commercial products presented as Comparative Examples which were known as common lubricants used for magnetic recording media, it was found that the 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature were higher than perfluoropolyether Z-DOL (Comparative Example 11C) by 100° C. or greater, and higher than Z-TETRAOL (Comparative Example 12C) by 50° C. or greater.

Example 2C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of bis(nonafluorobutanesulfonyl)imide-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene were 341.1° C., 372.9° C., and 396.3° C., respectively. It was found that thermal stability was improved by 100° C. or greater compared with perfluoropolyether Z-DOL (Comparative Example 11C) or Z-TETRAOL (Comparative Example 12C) that was a commercial product.

Example 3C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of nonafluorobutanesulfonic acid-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene were 346.9° C., 373.1° C., and 396.8° C., respectively. Compared to the commercial products presented as Comparative Examples which were known as common lubricants used for magnetic recording media, it was found that the 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature were higher than perfluoropolyether Z-DOL (Comparative Example 11C) by 150° C. or greater, and higher than Z-TETRAOL (Comparative Example 12C) by 100° C. or greater.

Example 4C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of bis(nonafluorobutanesulfonyl)imide-N-butyl-N-octadecylpyrrolidinium were 331.4° C., 360.2° C., and 382.5° C., respectively. It was found that thermal stability was improved by 90° C. or greater compared with perfluoropolyether Z-DOL (Comparative Example 11C) or Z-TETRAOL (Comparative Example 12C) that was a commercial product.

Example 5C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of bis(nonafluorobutanesulfonyl)imide-N-octadecylpyrrolidinium were 312.6° C., 334.4° C., and 355.5° C., respectively. It was found that thermal stability was improved by 70° C. or greater compared with perfluoropolyether Z-DOL (Comparative Example 11C) or Z-TETRAOL (Comparative Example 12C) that was a commercial product.

Example 6C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of nonafluorobutanesulfonic acid-N-octadecylpyrrolidinium were 339.4° C., 359.0° C., and 377.3° C., respectively. It was found that thermal stability was improved by 95° C. or greater compared with perfluoropolyether Z-DOL (Comparative Example 11C) or Z-TETRAOL (Comparative Example 12C) that was a commercial product.

Example 7C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of trifluoromethanesulfonic acid-8-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium were 319.2° C., 346.6° C., and 389.0° C., respectively. Compared to the commercial products presented as Comparative Examples which were known as common lubricants used for magnetic recording media, it was found that the 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature were higher than perfluoropolyether Z-DOL (Comparative Example 11C) by 140° C. or greater, and higher than Z-TETRAOL (Comparative Example 12C) by 80° C. or greater.

Example 8C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of bis(nonafluorobutanesulfonyl)imide-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-octadecylimidazolium were 335.8° C., 358.5° C., and 377.7° C., respectively. Compared to perfluoropolyether Z-DOL (Comparative Example 11C) and Z-TETRAOL (Comparative Example 12C) of the commercial products, it was found that thermal stability was improved by 150° C. or greater, and 90° C. or greater, respectively.

Example 9C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of bis(nonafluorobutanesulfonyl)imide-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-methylimidazolium were 350.3° C., 365.5° C., and 381.3° C., respectively. Compared to the commercial products presented as Comparative Examples which were known as common lubricants used for magnetic recording media, it was found that the 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature were higher than perfluoropolyether Z-DOL (Comparative Example 11C) by 150° C. or greater, and higher than Z-TETRAOL (Comparative Example 12C) by 90° C. or greater.

Example 10C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of nonafluorobutanesulfonic acid-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-methylimidazolium were 373.8° C., 389.3° C., and 401.7° C., respectively. Compared to perfluoropolyether Z-DOL (Comparative Example 11C) and Z-TETRAOL (Comparative Example 12C) of the commercial products, it was found that thermal stability was improved by 170° C. or greater, and 120° C. or greater, respectively.

Example 11C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of 1,3-bis[bis(nonafluorobutanesulfonyl)imide-N-octadecylimidazolium)]propane were 352.3° C., 381.9° C., and 401.4° C., respectively. Compared to perfluoropolyether Z-DOL (Comparative Example 11C) and Z-TETRAOL (Comparative Example 12C) of the commercial products, it was found that thermal stability was improved by 170° C. or greater, and 120° C. or greater, respectively.

Comparative Example 1C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of hexafluorocyclopropane-1,3-bis(sulfonyl)imide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium were 346.3° C., 384.1° C., and 414.0° C., respectively. Since hexafluorocyclopropane-1,3-bis(sulfonyl)imide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium was an ionic liquid, thermal stability was high compared to perfluoropolyether Z-DOL (Comparative Example 11C) or Z-TETRAOL (Comparative Example 12C) of the commercial product.

Comparative Example 2C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of heptadecafluorooctanesulfonic acid-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium were 361.9° C., 382.7° C., and 403.5° C., respectively. Since heptadecafluorooctanesulfonic acid-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium was an ionic liquid, thermal stability was high compared to perfluoropolyether Z-DOL (Comparative Example 11C) or Z-TETRAOL (Comparative Example 12C) of the commercial product.

Comparative Example 3C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of tris(trifluoromethanesulfonyl)methide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium were 354.9° C., 385.0° C., and 404.3° C., respectively. Since tris(trifluoromethanesulfonyl)methide-6-octadecyl-1,8-diazabicyclo[5.4.0]-7-undecenium was an ionic liquid, thermal stability was high compared to perfluoropolyether Z-DOL (Comparative Example 11C) or Z-TETRAOL (Comparative Example 12C) of the commercial product.

Comparative Example 4C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of hexafluorocyclopropane-1,3-bis(sulfonyl)imide-7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decenium were 288.4° C., 376.2° C., and 412.1° C., respectively. Since hexafluorocyclopropane-1,3-bis(sulfonyl)imide-7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decenium was an ionic liquid, thermal stability was high compared to perfluoropolyether Z-DOL (Comparative Example 11C) or Z-TETRAOL (Comparative Example 12C) of the commercial product.

Comparative Example 5C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of heptadecafluorooctanesulfonic acid-7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decenium were 356.1° C., 380.4° C., and 401.5° C., respectively. Since heptadecafluorooctanesulfonic acid-7-octadecyl-1,5,7-triazabicyclo[4.4.0]-5-decenium was an ionic liquid, thermal stability was high compared to perfluoropolyether Z-DOL (Comparative Example 11C) or Z-TETRAOL (Comparative Example 12C) of the commercial product.

Comparative Example 6C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of hexafluorocyclopropane-1,3-bis(sulfonyl)imide-N-octadecylpyrrolidinium were 336.4° C., 358.4° C., and 379.4° C., respectively. Since hexafluorocyclopropane-1,3-bis(sulfonyl)imide-N-octadecylpyrrolidinium was an ionic liquid, thermal stability was high compared to perfluoropolyether Z-DOL (Comparative

Example 11C) or Z-TETRAOL (Comparative Example 12C) of the commercial product.

Comparative Example 7C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of nonafluorobutanesulfonic acid-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-octadecylimidazolium were 257.5° C., 267.6° C., and 278.4° C., respectively. Since nonafluorobutanesulfonic acid-1-1′H,1′H,2′H,2′H-heptadecafluorodecyl-3-octadecylimidazolium was an ionic liquid, thermal stability was high compared to perfluoropolyether Z-DOL (Comparative Example 11C) or Z-TETRAOL (Comparative Example 12C) of the commercial product.

Comparative Example 8C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of bis(nonafluorobutanesulfonyl)imide-1 l-butyl-3-n-octadecylimidazolium were 347.2° C., 367.0° C., and 387.8° C., respectively. Since bis(nonafluorobutanesulfonyl)imide-1-butyl-3-n-octadecylimidazolium was an ionic liquid, thermal stability was high compared to perfluoropolyether Z-DOL (Comparative Example 11C) or Z-TETRAOL (Comparative Example 12C) of the commercial product.

Comparative Example 9C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of 1,5-bis[bis(nonafluorobutanesulfonyl)imide-1-octadecylimidazolium]pentane were 360.1° C., 384.4° C., and 402.0° C., respectively. Since 1,5-bis[bis(nonafluorobutanesulfonyl)imide-1-octadecylimidazolium]pentane was an ionic liquid, compared to perfluoropolyether Z-DOL (Comparative Example 11C) and Z-TETRAOL (Comparative Example 12C) of the commercial products, thermal stability was higher by 170° C. or greater, and 120° C. or greater, respectively.

Comparative Example 10C <Thermal Stability Measurement Results>

The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of 1,9-bis[bis(nonafluorobutanesulfonyl)imide-1-octadecylimidazolium]nonane were 355.1° C., 381.0° C., and 400.9° C., respectively. Since 1,9-bis[bis(nonafluorobutanesulfonyl)imide-1-octadecylimidazolium]nonane was an ionic liquid, compared to perfluoropolyether Z-DOL (Comparative Example 11C) and Z-TETRAOL (Comparative Example 12C) of the commercial products, thermal stability was higher by 170° C. or greater, and 110° C. or greater, respectively.

Comparative Example 11C <Thermal Stability Measurement Results>

As Comparative Example 11C, measurements of a commercial product, perfluoropolyether Z-DOL that had a hydroxyl group at a terminal and had a molecular weight of about 2,000 were performed. As a result, the 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of perfluoropolyether Z-DOL were 165.0° C., 197.0° C., and 226.0° C., respectively. The weight reduction was caused by evaporation.

Comparative Example 12C <Thermal Stability Measurement Results>

Perfluoropolyether (Z-TETRAOL) that was a commercial product and was typically used as a lubricant for magnetic recording media was used as a lubricant of Comparative Example 12C. Perfluoropolyether (Z-TETRAOL) had a plurality of hydroxyl groups at terminals and had a molecular weight of about 2,000. The 5% weight reduction temperature, 10% weight reduction temperature, and 20% weight reduction temperature of Z-TETRAOL were 240.0° C., 261.0° C., and 282.0° C., respectively. Similarly to Z-DOL, the weight reduction was caused by evaporation.

The results of Examples 1C to 11C and Comparative Examples 1C to 12C are summarized in Table 4.

TABLE 4 Synthesis Example or name of Weight reduction temperature (° C.) Example compound 5% 10% 20% Ex. 1C Ex. 1A 352.9 378.2 396.7 Ex. 2C Ex. 2A 341.1 372.9 396.3 Ex. 3C Ex. 3A 346.9 373.1 396.8 Ex. 4C Ex. 4A 331.4 360.2 382.5 Ex. 5C Ex. 5A 312.6 334.4 355.5 Ex. 6C Ex. 6A 339.4 359.0 377.3 Ex. 7C Ex. 7A 319.2 346.6 389.0 Ex. 8C Ex. 8A 335.8 358.5 377.7 Ex. 9C Ex. 9A 350.3 365.5 381.3 Ex. 10C Ex. 10A 373.8 389.3 401.7 Ex. 11C Ex. 11A 352.3 381.9 401.4 Comp. Ex. 1C Comp. Ex. 1A 346.3 384.1 414.0 Comp. Ex. 2C Comp. Ex. 2A 361.9 382.7 403.5 Comp. Ex. 3C Comp. Ex. 3A 354.9 385.0 404.3 Comp. Ex. 4C Comp. Ex. 4A 288.4 376.2 412.1 Comp. Ex. 5C Comp. Ex. 5A 356.1 380.4 401.5 Comp. Ex. 6C Comp. Ex. 6A 336.4 358.4 379.4 Comp. Ex. 7C Comp. Ex. 7A 257.5 267.6 278.4 Comp. Ex. 8C Comp. Ex. 8A 347.2 367.0 387.8 Comp. Ex. 9C Comp. Ex. 9A 360.1 384.4 402.0 Comp. Ex. 10C Comp. Ex. 10A 355.1 381.0 400.9 Comp. Ex. 11C Z-DOL 165.0 197.0 226.0 Comp. Ex. 12C Z-Tetraol 240.0 261.0 282.0

As demonstrated above, it was found that the ionic liquid-based lubricants excelled in thermal stability compared to the polyfluoropolyether of the commercial products of Comparative Examples 11C and 12C.

With comparing thermal stability between the ionic liquids, the thermal stability of the ionic liquids each having the octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene structure can be compared using Examples 1C to 3C, Example 7C, and Comparative Examples 1C to 3C. In this comparison, the weight reduction temperatures of Comparative examples were higher by about 10° C. to about 50° C. However, the ionic liquid having the octadecyl-1,8-diazabicyclo[5.4.0]-7-undecene structure had significantly high weight reduction temperatures, the 20% weight reduction temperature was close to 400° C., hence was considered to have sufficient thermal stability.

Moreover, Examples 4C to 6C were compared to Comparative Example 6C for the ionic liquids each having the N-octadecylpyrrolidine structure, and it was found that there was no significant difference in thermal stability between Examples and Comparative Example. As described above, Comparative Example 6C exhibited extremely high thermal stability compared to the polyfluoropolyether structure of the commercial product, because Comparative Example 6C was the ionic liquid.

Moreover, Examples 8C to 11C were compared to Comparative Examples 7C to 10C for the ionic liquids each having the imidazole structure. Excluding Comparative Example 7C, there was no significant difference in thermal stability between Examples and Comparative Examples. As described above, Comparative Examples 8C to 10C exhibited extremely high thermal stability compared to the polyfluoropolyether structure of the commercial product, because Comparative Examples 8C to 10C were the ionic liquids.

Examples 1D to 11D, and Comparative Examples 1D to 10D <Disk Durability Test>

Magnetic disks were each produced by applying a lubricant including each of the ionic liquids of Examples 1A to 11A and Comparative Examples 1A to 10A. As presented in Tables 5-1 and 5-2, the CSS measurements of the magnetic disks were greater than 50,000 times, and the CSS measurements after the heating tests were also greater than 50,000 times, hence excellent durability was exhibited.

Comparative Example 11D <Disk Durability Test>

The above-described magnetic disk was produced using a lubricant including Z-DOL. As presented in Table 5-2, the CSS measurement of the magnetic disk was greater than 50,000 times, but the CSS measurement after the heating test was 12,000 times and the durability was deteriorated further by the heating test.

Comparative Example 12D <Disk Durability Test>

The above-described magnetic disk was produced using a lubricant including Z-TETRAOL. As presented in Table 5-2, the CSS measurement of the magnetic disk was greater than 50,000 times, but the CSS measurement after the heating test was 36,000 times and the durability was deteriorated further by the heating test.

The results of Examples 1D to 11D and Comparative Examples 1D to 12D are summarized in Tables 5-1 and 5-2.

TABLE 5-1 Synthesis Example or name of CSS durability compound CSS durability after heating Ex. 1D Ex. 1A 25° C., >50,000 25° C., >50,000 60% RH 60% RH Ex. 2D Ex. 2A 25° C., >50,000 25° C., >50,000 60% RH 60% RH Ex. 3D Ex. 3A 25° C., >50,000 25° C., >50,000 60% RH 60% RH Ex. 4D Ex. 4A 25° C., >50,000 25° C., >50,000 60% RH 60% RH Ex. 5D Ex. 5A 25° C., >50,000 25° C., >50,000 60% RH 60% RH Ex. 6D Ex. 6A 25° C., >50,000 25° C., >50,000 60% RH 60% RH Ex. 7D Ex. 7A 25° C., >50,000 25° C., >50,000 60% RH 60% RH Ex. 8D Ex. 8A 25° C., >50,000 25° C., >50,000 60% RH 60% RH Ex. 9D Ex. 9A 25° C., >50,000 25° C., >50,000 60% RH 60% RH Ex. 10D Ex. 10A 25° C., >50,000 25° C., >50,000 60% RH 60% RH Ex. 11D Ex. 11A 25° C., >50,000 25° C., >50,000 60% RH 60% RH

TABLE 5-2 Synthesis Example or name of CSS durability compound CSS durability after heating Comp. Comp. 25° C., >50,000 25° C., >50,000 Ex. 1D Ex. 1A 60% RH 60% RH Comp. Comp. 25° C., >50,000 25° C., >50,000 Ex. 2D Ex. 2A 60% RH 60% RH Comp. Comp. 25° C., >50,000 25° C., >50,000 Ex. 3D Ex. 3A 60% RH 60% RH Comp. Comp. 25° C., >50,000 25° C., >50,000 Ex. 4D Ex. 4A 60% RH 60% RH Comp. Comp. 25° C., >50,000 25° C., >50,000 Ex. 5D Ex. 5A 60% RH 60% RH Comp. Comp. 25° C., >50,000 25° C., >50,000 Ex. 6D Ex. 6A 60% RH 60% RH Comp. Comp. 25° C., >50,000 25° C., >50,000 Ex. 7D Ex. 7A 60% RH 60% RH Comp. Comp. 25° C., >50,000 25° C., >50,000 Ex. 8D Ex. 8A 60% RH 60% RH Comp. Comp. 25° C., >50,000 25° C., >50,000 Ex. 9D Ex. 9A 60% RH 60% RH Comp. Comp. 25° C., >50,000 25° C., >50,000 Ex. 10D Ex. 10A 60% RH 60% RH Comp. Z-DOL 25° C., >50,000 25° C., 12,000 Ex. 11D 60% RH 60% RH Comp. Z-Tetraol 25° C., >50,000 25° C., 36,000 Ex. 12D 60% RH 60% RH

Examples 1E to 11E and Comparative Examples 25 to 12E

The above-described magnetic tapes were each produced by using a lubricant including each of the ionic liquids of Examples A to 60% RHA, the ionic liquids of Comparative Examples 1A to 10A, Z-DOL, and Z-TETRAOL. Then, the following measurements were performed. The results are presented in Tables 6-1 and 6-2.

Coefficient of friction of magnetic tape after shuttle run of 100 times:

In the environment having a temperature of −5° C., or in the environment having a temperature of 40° C. and relative humidity of 90%.

Still durability test:

In the environment having a temperature of −5° C., or in the environment having a temperature of 40° C. and relative humidity of 30%.

Shuttle durability test:

In the environment having a temperature of −5° C., or in the environment having a temperature of 40° C. and relative humidity of 90%.

Coefficient of friction of magnetic tape after shuttle run of 100 times after heating test:

In the environment having a temperature of −5° C., or in the environment having a temperature of 40° C. and relative humidity of 90%.

Still durability test after heating test:

In the environment having a temperature of −5° C., or in the environment having a temperature of 40° C. and relative humidity of 30%.

Shuttle durability test after heating test:

In the environment having a temperature of −5° C., or in the environment having a temperature of 40° C. and relative humidity of 90%.

The results of Examples 1E to 11E and Comparative Examples 1E to 12E are summarized in Tables 6-1 and 6-2.

TABLE 6-1 Friction Friction Still Shuttle coefficient Still Shuttle coefficient durability durability after 100 durability/ durability/ after 100 runs after heating/ after heating/ Compound runs min times after heating min times Ex. 1E Ex. 1A −5° C. 0.22 −5° C. >60 −5° C. >200 −5° C. 0.23 −5° C. >60 −5° C. >200 40° C., 0.25 40° C., >60 40° C., >200 40° C., 0.26 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Ex. 2E Ex. 2A −5° C. 0.22 −5° C. >60 −5° C. >200 −5° C. 0.23 −5° C. >60 −5° C. >200 40° C., 0.24 40° C., >60 40° C., >200 40° C., 0.24 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Ex. 3E Ex. 3A −5° C. 0.21 −5° C. >60 −5° C. >200 −5° C. 0.22 −5° C. >60 −5° C. >200 40° C., 0.23 40° C., >60 40° C., >200 40° C., 0.23 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Ex. 4E Ex. 4A −5° C. 0.24 −5° C. >60 −5° C. >200 −5° C. 0.23 −5° C. >60 −5° C. >200 40° C., 0.26 40° C., >60 40° C., >200 40° C., 0.26 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Ex. 5E Ex. 5A −5° C. 0.24 −5° C. >60 −5° C. >200 −5° C. 0.24 −5° C. >60 −5° C. >200 40° C., 0.25 40° C., >60 40° C., >200 40° C., 0.26 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Ex. 6E Ex. 6A −5° C. 0.23 −5° C. >60 −5° C. >200 −5° C. 0.22 −5° C. >60 −5° C. >200 40° C., 0.24 40° C., >60 40° C., >200 40° C., 0.25 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Ex. 7E Ex. 7A −5° C. 0.22 −5° C. >60 −5° C. >200 −5° C. 0.23 −5° C. >60 −5° C. >200 40° C., 0.25 40° C., >60 40° C., >200 40° C., 0.26 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Ex. 8E Ex. 8A −5° C. 0.21 −5° C. >60 −5° C. >200 −5° C. 0.22 −5° C. >60 −5° C. >200 40° C., 0.23 40° C., >60 40° C., >200 40° C., 0.23 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Ex. 9E Ex. 9A −5° C. 0.25 −5° C. >60 −5° C. >200 −5° C. 0.26 −5° C. >60 −5° C. >200 40° C., 0.27 40° C., >60 40° C., >200 40° C., 0.28 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Ex. 10E Ex. 10A −5° C. 0.25 −5° C. >60 −5° C. >200 −5° C. 0.25 −5° C. >60 −5° C. >200 40° C., 0.28 40° C., >60 40° C., >200 40° C., 0.28 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Ex. 11E Ex. 11A −5° C. 0.19 −5° C. >60 −5° C. >200 −5° C. 0.20 −5° C. >60 −5° C. >200 40° C., 0.20 40° C., >60 40° C., >200 40° C., 0.20 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH

TABLE 6-2 Friction Still Shuttle Friction Still Shuttle coefficient durability durability after coefficient durability/ durability/ after 100 runs after heating/ heating/ Compound after 100 runs min times after heating min times Comp. Comp. −5° C. 0.23 −5° C. >60 −5° C. >200 −5° C. 0.24 −5° C. >60 −5° C. >200 Ex. 1E Ex. 1A 40° C., 0.26 40° C., >60 40° C., >200 40° C., 0.27 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Comp. Comp. Ex. −5° C. 0.22 −5° C. >60 −5° C. >200 −5° C. 0.24 −5° C. >60 −5° C. >200 Ex. 2E 2A 40° C., 0.26 40° C., >60 40° C., >200 40° C., 0.26 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Comp. Comp. −5° C. 0.21 −5° C. >60 −5° C. >200 −5° C. 0.21 −5° C. >60 −5° C. >200 Ex. 3E Ex. 3A 40° C., 0.21 40° C., >60 40° C., >200 40° C., 0.22 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Comp. Comp. −5° C. 0.23 −5° C. >60 −5° C. >200 −5° C. 0.24 −5° C. >60 −5° C. >200 Ex. 4E Ex. 4A 40° C., 0.27 40° C., >60 40° C., >200 40° C., 0.27 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Comp. Comp. −5° C. 0.24 −5° C. >60 −5° C. >200 −5° C. 0.24 −5° C. >60 −5° C. >200 Ex. 5E Ex. 5A 40° C., 0.28 40° C., >60 40° C., >200 40° C., 0.28 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Comp. Comp. −5° C. 0.23 −5° C. >60 −5° C. >200 −5° C. 0.24 −5° C. >60 −5° C. >200 Ex. 6E Ex. 6A 40° C., 0.25 40° C., >60 40° C., >200 40° C., 0.26 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Comp. Comp. −5° C. 0.21 −5° C. >60 −5° C. >200 −5° C. 0.21 −5° C. >60 −5° C. >200 Ex. 7E Ex. 7A 40° C., 0.22 40° C., >60 40° C., >200 40° C., 0.22 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Comp. Comp. −5° C. 0.22 −5° C. >60 −5° C. >200 −5° C. 0.23 −5° C. >60 −5° C. >200 Ex. 8E Ex. 8A 40° C., 0.24 40° C., >60 40° C., >200 40° C., 0.25 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Comp. Comp. −5° C. 0.18 −5° C. >60 −5° C. >200 −5° C. 0.2 −5° C. >60 −5° C. >200 Ex. 9E Ex. 9A 40° C., 0.19 40° C., >60 40° C., >200 40° C., 0.2 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Comp. Comp. −5° C. 0.18 −5° C. >60 −5° C. >200 −5° C. 0.19 −5° C. >60 −5° C. >200 Ex. 10E Ex. 10A 40° C., 0.19 40° C., >60 40° C., >200 40° C., 0.19 40° C., >60 40° C., >200 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Comp. Z-DOL −5° C. 0.25 −5° C. 12 −5° C. 59 −5° C. 0.32 −5° C. 12 −5° C. 46 Ex. 11E 40° C., 0.30 40° C., 48 40° C., 124 40° C., 0.35 40° C., 15 40° C., 58 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH Comp. Z- −5° C. 0.22 −5° C. 25 −5° C. 65 −5° C. 0.28 −5° C. 23 −5° C. 55 Ex. 12E TETRAOL 40° C., 0.26 40° C., 35 40° C., 156 40° C., 0.32 40° C., 31 40° C., 126 90% RH 30% RH 90% RH 90% RH 30% RH 90% RH

In the tables above, “>60” of the still durability denotes greater than 60 minutes.

In the tables above, “>200” of the shuttle durability denotes greater than 200 times.

The following facts were confirmed.

It was found that the magnetic tapes to which the lubricants including the ionic liquids of Examples 1A to 11A were applied had excellent friction properties, still durability, and shuttle durability.

It was found that the magnetic tapes to which the lubricants including the ionic liquids of Comparative Examples 1A to 10A were applied had excellent friction properties, still durability, and shuttle durability. Since the lubricants of Comparative Examples 1A to 10A were ionic liquids, excellent tape durability was exhibited even after the heating test.

It was found that the magnetic tape to which Z-DOL was applied had significant deteriorations in still durability and shuttle durability.

It was found that the magnetic tape to which Z-TETRAOL was applied had significant deteriorations in still durability and shuttle durability.

It was found from Tables 6-1 and 6-2 that excellent heat resistance, and durability of a magnetic tape and a magnetic disk were obtained by using an ionic liquid-based lubricant, which included an ionic liquid including a conjugate base and a conjugate acid where the conjugate acid had a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, a pKa of an acid that was a source of the conjugate base in acetonitrile was 10 or less, and solubility of the ionic liquid to CF₃(CHF)₂CF₂CF₃ was 0.1 parts by mass or greater relative to 100 parts by mass of CF₃(CHF)₂CF₂CF₃. Since the ionic liquid was also dissolved to a fluorine-based solvent, moreover, not only having excellent heat resistance and durability of magnetic recording media, there was no problem in a production process, particularly when the ionic liquid-based lubricant was applied for a hard disk.

As it is clear from the descriptions above, an ionic liquid-based lubricant, which includes an ionic liquid including a conjugate base and a conjugate acid, where the conjugate acid has a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, a pKa of an acid that is a source of the conjugate base in acetonitrile is 10 or less, and solubility of the ionic liquid to CF₃(CHF)₂CF₂CF₃ is 0.1 parts by mass or greater relative to 100 parts by mass of CF₃(CHF)₂CF₂CF₃, has a high decomposition temperature and high 5%, 10%, and 20% weight reduction temperatures and has excellent thermal stability. Moreover, the ionic liquid-based lubricant can maintain excellent lubricity in high temperature conditions compared to conventional perfluoropolyether, and can also maintain lubricity over a long period. Accordingly, a magnetic recording medium using the above-mentioned lubricant including the ionic liquid can obtain significantly excellent running performances, abrasion resistance, and durability. Since the ionic liquid is dissolved in a fluorine-based solvent, moreover, there is no problem in a production process, particularly when the lubricant including the ionic liquid is applied for a hard disk.

REFERENCE SINGS LIST

-   11: substrate -   12: base layer -   13: magnetic layer -   14: carbon protective layer -   15: lubricant layer -   21: substrate -   22: magnetic layer -   23: carbon protective layer -   24: lubricant layer -   25: back-coating layer 

1. A lubricant comprising: an ionic liquid including a conjugate base and a conjugate acid, wherein the conjugate acid has a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, a pKa of an acid that is a source of the conjugate base in acetonitrile is 10 or less, and solubility of the ionic liquid to CF₃(CHF)₂CF₂CF₃ is 0.1 parts by mass or greater relative to 100 parts by mass of CF₃(CHF)₂CF₂CF₃.
 2. The lubricant according to claim 1, wherein the conjugate acid is represented by General Formula (A) below, General Formula (B) below, General Formula (C) below, General Formula (D) below, General Formula (E) below, or General Formula (F) below,

where, in General Formula (A), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and R² is a hydrogen atom or a hydrocarbon group, in General Formula (B), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, in General Formula (C), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, in General Formula (D), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and R² is a hydrogen atom or a hydrocarbon group, in General Formula (E), R³ is a hydrocarbon group, R⁴ is a hydrogen atom or a hydrocarbon group, and R⁵ is a group including a C8 or higher fluorinated hydrocarbon group including fluorinated hydrocarbon having 4 or more carbon atoms, and in General Formula (F), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and n is an integer of 1 or greater but 3 or less.
 3. The lubricant according to claim 1, wherein the conjugate base is represented by General Formula (X) below, General Formula (Y) below, or General Formula (Z) below,

where, in General Formula (X), l is an integer of 1 or greater but 12 or less, in General Formula (Y), n is an integer of 1 or greater but 12 or less, and in General Formula (Z), n is an integer of 0 or greater but 6 or less.
 4. A magnetic recording medium comprising: a non-magnetic support; a magnetic layer disposed on the non-magnetic support; and the lubricant according to claim 1, disposed on the magnetic layer.
 5. An ionic liquid comprising: a conjugate base; and a conjugate acid, wherein the conjugate acid has a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, a pKa of an acid that is a source of the conjugate base in acetonitrile is 10 or less, and solubility of the ionic liquid to CF₃(CHF)₂CF₂CF₃ is 0.1 parts by mass or greater relative to 100 parts by mass of CF₃(CHF)₂CF₂CF₃.
 6. The ionic liquid according to claim 5, wherein the conjugate acid is represented by General Formula (A) below, General Formula (B) below, General Formula (C) below, General Formula (D) below, General Formula (E) below, or General Formula (F) below,

where, in General Formula (A), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and R² is a hydrogen atom or a hydrocarbon group, in General Formula (B), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, in General Formula (C), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, in General Formula (D), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and R² is a hydrogen atom or a hydrocarbon group, in General Formula (E), R³ is a hydrocarbon group, R⁴ is a hydrogen atom or a hydrocarbon group, R⁵ is a group including C8 or higher fluorinated hydrocarbon group including fluorinated hydrocarbon having 4 or more carbon atoms, and in General Formula (F), R¹ is a group including a straight-chain hydrocarbon group having 6 or more carbon atoms, and n is an integer of 1 or greater but 3 or less.
 7. The ionic liquid according to claim 5, wherein the conjugate base is represented by General Formula (X) below, General Formula (Y) below, or General Formula (Z) below,

where, in General Formula (X), l is an integer of 1 or greater but 12 or less, in General Formula (Y), n is an integer of 1 or greater but 12 or less, and in General Formula (Z), n is an integer of 0 or greater but 6 or less. 